In November 2011, Paul Frampton, a theoretical particle physicist, met Denise Milani, a Czech bikini model, on the online dating site mate1.com. She was gorgeous – dark-haired and dark-eyed, with a supposedly natural DDD breast size. In some photos, she looked tauntingly steamy; in others, she offered a warm smile.

Soon, they were chatting online nearly every day. He would return home from campus – he had been a professor in the physics and astronomy department at the University of North Carolina for 30 years – and his computer would buzz. "Are you there, honey?" They'd chat on Yahoo Messenger for a while, then he'd go to the other room to take care of something. A half-hour later, there was the familiar buzz. It was always Milani: "What are you doing now?"

Frampton had been lonely since his divorce three years earlier; now it seemed those days were over. Milani told him she was longing to change her life. She was tired of being a glamour model, of posing in her bikini on the beach while men ogled. She wanted to settle down, have children. But she worried what he thought of her: "Do you think you could ever be proud of someone like me?" Of course he could, he assured her.

Frampton tried to get her to talk on the phone, but she always demurred. When she finally agreed to meet him in person, she asked him to come to La Paz, Bolivia, where she was on a photoshoot. On 7 January 2012, he set out for Bolivia via Toronto and Santiago, Chile. At 68, he dreamed of finding a wife to bear him children – and what a wife. He pictured introducing Milani to colleagues. One thing worried him, though. She had told him that men hit on her all the time. How did that affect her? Did it go to her head? But then he remembered how comforting it felt to chat with her, like having a companion in the next room. And he knew she loved him. She'd said so many times.

Frampton didn't plan on a long trip – he needed to be back to teach – so he left his car at the airport. Soon, he hoped, he'd be returning with Milani on his arm. The first thing that went wrong was that the e-ticket she had sent for the Toronto-Santiago leg of his journey turned out to be invalid, leaving him stranded in Toronto for a full day. Frampton finally arrived in La Paz four days after he had set off. He hoped to meet Milani the next morning, but she had been called away to another photoshoot in Brussels. She promised to send him a ticket to join her there, so Frampton, who had checked into the Eva Palace hotel, worked on a paper while he waited for it to arrive. A ticket to Buenos Aires eventually came, with the promise that a ticket to Brussels was on the way. All Milani asked was that Frampton do her a favour: bring her a bag that she had left in La Paz.

While in Bolivia, Frampton corresponded with an old friend, John Dixon, a physicist and lawyer. When Frampton explained what he was up to, Dixon became alarmed. His warnings were unequivocal: "I said, 'Inside that suitcase, sewn into the lining, will be cocaine. You're in big trouble.' Paul said, 'I'll be careful. I'll make sure there isn't cocaine in there, and if there is I'll ask them to remove it.' I thought they were probably going to kidnap him and torture him to get his money. I didn't know he didn't have money. I said, 'Well, you're going to be killed, so whom should I contact when you disappear?' And he said, 'My brother and my former wife.' " Frampton later told me that he shrugged off Dixon's warnings as melodramatic, adding that he rarely pays attention to the opinions of others.

On the evening of 20 January, a man Frampton describes as Hispanic, but whom he didn't get a good look at, handed him a bag on the dark street in front of his hotel. Frampton was expecting a Hermès or Louis Vuitton, but the bag was a commonplace black cloth suitcase with wheels. Back in his room, he opened it. It was empty. He wrote to Milani, asking why this case was so important. She told him it had "sentimental value". The next morning, he filled it with his dirty laundry and headed to the airport.

Frampton flew to Buenos Aires, crossing the border without incident. He says he spent the next 40 hours in Ezeiza airport mainly "doing physics" and checking his email in the hope that an e-ticket to Brussels would arrive. But by the time it materialised, Frampton had already asked a friend to send him a ticket to Raleigh: he had been away for 15 days and was ready to go home. There was always the chance that Milani would come to North Carolina and want her bag, so he checked in two bags, his and hers, and went to the gate. Soon he heard his name called on the loudspeaker. He thought it must be for an upgrade, but when he got to the airline counter, he was greeted by several policemen. Asked to identify his luggage – "That's my bag, the other one's not mine, but I checked it in" – he waited while they tested the contents of a package found in Milani's suitcase. Within hours, he was under arrest.

I met Frampton last autumn, in the warden's office in Devoto prison, one of the few remaining old-style jails in Buenos Aires, and so dilapidated that its windows stick open and rain leaks through the roof. It was September, the start of spring in the southern hemisphere, but there was a chill in the air and the heating system was down as usual.

"Hey, professor, have you won the Nobel yet?" a guard shouted as Frampton walked by. He was wearing a red Adidas tracksuit, running shoes and a tattered Barbour coat to keep warm. "This is the coat the royal family wears – it's for hunting," Frampton pointed out. "See, it has this pocket in the back where you can put a dead bird." He had been in Devoto for eight months, awaiting trial on charges of transporting 2kg of cocaine into the country. He was housed in a group pavilion with 80 men accused of drug dealing or smuggling, most of them from other Latin American countries. Frampton had had almost no experience with drugs, apart from the occasional drink and nicotine. Now he was living with people who were not only well versed in the intricacies of the drug trade, but regular users of marijuana and cocaine. The pavilion was often illuminated at night by little flames held under spoons, as inmates cooked paco, a cocaine paste similar to crack that is often made with kerosene and sulphuric acid. But there were good things about not being in a private cell. Several prisoners had their own TVs. On Sunday mornings, Frampton would turn on the classical music station for a few hours before others got up and switched back to music videos. Whenever his case was reported on local news, pictures of Milani would flash across the screen, eliciting catcalls and applause from other prisoners. "I'm a bit of a celebrity in here," Frampton told me.

From the moment of his arrest, he had maintained that he was the victim of a scam, and he projected a sense that all that had happened to him was a mistake that would soon be resolved. Perfectly congenial, he kept punctuating my questions about his present predicament with, "And after this we'll get to physics, right?"

Finally, eyes burning with schoolboy enthusiasm, interrupted now and then by a spasmodic cough – he has a lung condition, which the smoke-filled prison air has made worse – he talked me through what he called his "14 groundbreaking discoveries", which he had written out for me on a piece of notepaper. He closed our interview half-seriously, half-impishly, with another kind of calculation: "I've co-authored with three Nobel laureates. Only 11 theoretical physicists have done that. Six out of those 11 have won Nobel prizes themselves. Following this logic, I have a 55% chance of getting the Nobel."

How Frampton, who holds an endowed chair at the University of North Carolina and has been an adviser to the US Department of Energy, ended up in Devoto appears at first to be a classic tale: a brilliant man of science gets into trouble as soon as he tries to navigate the real world. Since his arrest, he has certainly cultivated this notion, burnishing his wacky-scientist profile with lines such as, "That's my naivety" and, "My mind works in a strange way."

Those who know him well portray him as a kind of idiot savant who could easily have been duped by whoever was posing as Milani. "Women came later in Paul's life," says Richard Czerniawski, who was a student with Frampton at Oxford University and now lives in Buenos Aires. Frampton was married for the first time at 50, to Anne-Marie, then 52, a Frenchwoman who calls herself a physics groupie: "I couldn't follow everything Paul said, because of the mathematics, of course, but either I could understand the words or I could just listen to the music, the music of physics." The pair divorced in 2008 but are on good terms. Anne-Marie describes her ex-husband as a very good scientist with the emotional age of a three-year-old. "I was flabbergasted. Flabbergasted but not surprised," she said, referring to the call he made to her from Devoto. "Paul is a very experienced traveller, but that line, 'Don't take any luggage that doesn't belong to you', he doesn't even hear that. He's in another world, an alternate universe."

One story about his search for a new wife certainly bolstered this view. Shortly after his divorce, Frampton, then 64, expressed concern about finding a wife between the ages of 18 and 35, which he understood to be when women are most fertile. One promising candidate was a young Chinese woman. After an extended email correspondence, Frampton arranged to see her during a trip to China to visit another eminent scientist, but they met for only an hour and "it didn't go anywhere". The next important contender appears to have been Milani. "He told me to look her up on the internet," Dixon said. "I thought he was out of his mind, and told him that. 'You're not talking to the real girl. Why would a young woman like that be interested in an old guy like you?' But he really believed that he had a pretty young woman who wanted to marry him." When I later asked Frampton what made him think Milani was interested, he replied, "Well, I have been accused of having a huge ego."

Over the course of three and a half months, Frampton called me 42 times from jail. He'd call to report the latest news. A "brilliant" op-ed he wrote in a Raleigh newspaper about the university provost's "illegal" action in cutting off his salary without due process had succeeded in getting the provost fired. (The provost had granted him 60 days of paid leave, then suspended his salary until he could resume his duties. Frampton sued the university, unsuccessfully, for his wages.) He was particularly pleased about the provost's dismissal, because the severance of his salary had had real repercussions. Apparently without savings, he was unable to afford a lawyer and had to rely on an overburdened Argentine public defender. He'd given up his health insurance, and risked losing his car and apartment in the US. In Argentina, he scrambled to get the money he needed to buy decent food in prison and phone cards, of which he might have as many as 30 in his pocket.

It turned out that the provost was stepping down voluntarily in June 2013 and would remain as a faculty member. Frampton didn't seem sheepish about having linked the provost's fate to his own. He was excited about something else now. The president of Harvard, he'd heard, had been given a memo about his case in the hope that she'd mention it to Argentina's president, Cristina Fernández de Kirchner, during Kirchner's visit to the university. "I think I've never been discussed by two such important people," Frampton said. (Harvard's president never received a memo about Frampton, and she and Kirchner never did discuss his case.) Or he'd report, ever hopefully, that he'd be out on house arrest any day. (His public attorney, Ignacio Anitua, had requested that his client be placed under house arrest, given his age and pulmonary ailment, but the request was still going through official channels.) He asked me to bring him gruyère, blue cheese, curry powder, chilli, notebooks, reading glasses and phone cards, and he expressed frustration about the slow progress of his case. He was especially exasperated that the text messages on his confiscated phone from 20 January had still not been handed over to his defence lawyer by the police. "It's clear from those messages that it was not my bag. That should be sufficient to exonerate me." (His lawyer told me the text messages were actually in his file, but would never be enough to prove his innocence.)

One Monday, Frampton called three times, the first at 3pm. He was animated and talked about the "volatile situation" at the university, which had yet to reinstate his salary despite letters of support from, among others, the Nobel laureate Sheldon Lee Glashow and John C Taylor, emeritus professor of physics at the University of Cambridge. "Research institutions throughout the country are in jeopardy if a tenured professor of 30 years has his salary suddenly revoked without any due process," he said. "This means that the jobs of tens of thousands of tenured professors are at risk."

Frampton claims he acted out of love for model Denise Milani, but it wasn't her chatting to him online

Second call, 6pm: Frampton reported that he was a month into his prison stay before his fellow prisoners managed to convince him that the woman he thought he'd been in touch with all this time had probably been a man impersonating her. The real Denise Milani was never accused of having a role in the drug smuggling and has no connection to Frampton. "The only real connection we have is through the international media," Frampton admitted. Milani has expressed alarm about having her name associated with drug smugglers, fear for herself and her 12-year-old son, and "sympathy" for the professor. "I feel sympathy for her, too," Frampton said.

Third call, 8pm: "There could be retribution. I could be assassinated." He spoke about how he had overheard the dealers and smugglers he was now living with talking about what happens to drug mules who lose the stash. He said people had told him someone must have been watching him at the airport, so they knew what he looked like. "These thoughts keep me up at night."

Frampton is prone to seeing himself as the centre of the action, whatever the milieu. When he was growing up in Worcestershire, England, in what he describes as a "lower-middle-class family", his mother encouraged him to report his stellar grades to the neighbours, a practice that may have led the young Frampton to confuse worldly laurels with love. At 18, he enrolled at Brasenose College, Oxford, obtaining a PhD in 1968. He received a number of offers for postdoctorates, including at Princeton and the University of Chicago. His advisers suggested he go to Chicago to work with the physicist Yoichiro Nambu. Nambu, who went on to win the Nobel prize in 2008, was a giant in the field, but Frampton's advisers may have had other reasons for steering him Nambu's way – Frampton told me he has "astonishingly no ego".

As Frampton tells it, his life is one unbroken line of impressive grades, advanced degrees and innumerable citations of his work. There is certainly much truth to this. "He has always been very inventive in thinking of new ideas extending and going beyond the standard model of particle physics," says Professor Edward Witten of the Institute for Advanced Study in Princeton. But then there is Frampton's tendency to transfer his professional accomplishments to his personal life. In what a fellow physicist described as a "very vain, very inappropriate" talk delivered on the 80th birthday of Murray Gell-Mann, a Nobel laureate in physics, Frampton veered into autobiography, recounting how his ability to multiply numbers in his head at four led him to see himself as "cleverer than Newton". This became a refrain throughout the talk. Interspersed with the calculations and hypotheses were his Oxford grades which, he said, showed that he, like Newton, was in the top 1 percentile for intelligence. Frampton insists that he was merely joking and that his sense of humour was misinterpreted as self-regard. Yet in many of our conversations, he seemed to cling to the idea of his own exceptionalism. At our first meeting, when I asked what attracted him to Milani, he said, "Not to offend present company", meaning me and the representative from the penitentiary service, "but, to start with, she's in the top 1 percentile of how women look." And in an email to Milani – or, rather, the fake Milani – he wrote, "As these days tick by, and I think about it a lot, the more I realise that we are the perfect couple in all respects."

The strategy of Frampton's defence team was to present him as a brilliant man who was out of touch with day-to-day life. They called in a psychologist, who pronounced him unusually gullible without diagnosing a mental illness. The judges sent their own doctor, who declared him normal. Three psychological evaluations were presented at trial, and two agreed that he had the traits of a narcissistic personality: an overblown, unrealistic image of himself. One concluded that it did not constitute a pathology, while the other suggested there were pathological aspects to his narcissism that led to gaps in his understanding of reality.

Fidel Schaposnik, a physics professor at the National University of La Plata – which, along with the University of Buenos Aires, offered Frampton a visiting professorship to help get him released from Devoto while awaiting trial – said, "He's a typical person trained at Oxford. He knows he's part of an elite and can't imagine such things would happen to him." Indeed, Frampton sees academia's denizens as creative misfits who deserve special protection. "People who are socially inept can nevertheless be the most creative people. It's very important that they can't be fired. This is the genius of tenure."

There has been another similar case in the past year, that of New Zealander Sharon Armstrong, a former executive at the Maori Language Commission. Like Frampton, she said she met her lover on an internet dating site and, after months of online contact, made a plan to meet him abroad, passing through Buenos Aires on her way to London, to pick up some paper contracts for him. She was caught with 5kg of cocaine. After the two were mentioned in a number of articles, Armstrong contacted Frampton. The judges in her case – she received a sentence of four years and 10 months – were also going to be the judges in his.

According to Rusty Payne, a spokesman for the US Drug Enforcement Administration, if Frampton and Armstrong were unaware of their involvement, they would be the exceptions. He had never heard of a case in which a virtual "honey trap" had been used to dupe someone into being an unwitting drug mule. "When it comes to drug trafficking, we rarely see someone duped or used as part of a ruse. It is very typical for those arrested to claim no knowledge or involvement." The prosecutor in Frampton's case – 80% of whose cases involve drug smuggling – concurred: it is highly improbable, he said, that a person is unaware that he or she is carrying drugs. Frampton acknowledged that this was undoubtedly true – most of the time. Of the other 79 prisoners on his pavilion, he thought none was innocent. "Some people will say they're innocent, but when I talk to them, it becomes clear that they were somehow involved. I think people like me are less than 1%."

Three weeks before his trial, Frampton hired private lawyers. When I asked how he was able to afford them, he first said he'd rather not tell me, then claimed that friends in Argentina were footing the bill. The new lawyers picked up where his public defenders left off, yet at a significantly accelerated pace. On 30 October, I spoke to Frampton as he was driving away from Devoto, accompanied by his friend Czerniawski, who had agreed to take him in on house arrest. Giddily, he said that the first thing he wanted to do was to sleep in, impossible in prison because every morning at 7.30 they do the roll call.

The following day at midday, I met Frampton at the Czerniawskis' apartment, just blocks from the Argentine parliament. Dressed in a dark blue pinstriped suit and a tie covered with tiny, red-beaked penguins, he was finishing lunch with Czerniawski's wife, Silvia, and their two daughters. "See," he said, "I'm Paul Frampton again." When I asked if he had slept in, he said he spent half the night on the internet, reading through the latest discoveries in his field, checking to see what his "competitors" had been working on, and beginning to answer thousands of emails. He reported that he had more citations than ever. The conversation turned to his long-awaited release to house arrest. How had the new lawyers achieved so quickly what his public attorney had been requesting for more than four months? "They say they drink maté with the judges," he answered cryptically. Later he added, "A little bird told me that if I get off, I'll never know why."

He showed me his latest calculations, pages of beautifully rendered symbols with not a word in sight except for "Nestor Kirchner", the former president and deceased husband of the current president, in the margin. "I'm trying to connect the God particle, the Higgs boson, with dark energy – you know, the thing that makes the universe accelerate. This sounds a bit egomaniacal, but to understand dark energy, I think we have to be open-minded about Einstein's general relativity."

This time, Frampton was the one who brought the conversation back to drug smuggling, showing palpable anxiety about the outcome of his trial. He told me uneasily that his lawyers had reported that nearly all drug smuggling cases that came to trial ended in guilty verdicts.

As I was leaving, he stepped out with me into the hallway. "Can I do this?" he asked, wondering if he was violating his house arrest. He got into the elevator, a wrought-iron cage that offered a view of the stairs as it descended, and repeated, "Can I do this?" He accompanied me down a long hall to the entrance and gave me a kiss goodbye on the cheek, peering out at the street as the door closed.

Two weeks later, on 12 November, Frampton's trial began in a small, wood-panelled courtroom, where he sat before three judges. On exhibit in front of the judges was a black cloth suitcase with wheels wrapped in yellow cellophane.

Frampton's defence – that he was duped because he had a childlike understanding of the ways of the world – began to unravel. The prosecutor opened his cross-examination by citing a text message retrieved from Frampton's confiscated phone. "On 22 January at 9.46am," he said, "you wrote from Ezeiza airport to the person you understood to be Denise Milani: 'Was worried only about sniffer dogs but more.' " As his interrogation continued, he read other text messages sent from Frampton's phone. One at 9.52am: "Need to know if your loyalty is with the bad guy-agent & bolivian friends – or good guy, your husband?" And another at 9.56am: "SIRU [the Hotel Siru, where they were planning to meet in Brussels] "IS AMBUSH." 10.14am: "Your naivety is bad for me, us. This is millions. NO SIRU, OK?" At 11.19am, Frampton sent Milani an email: "This stuff is worth nothing in Bolivia, but $Ms in Europe. You meet me at the airport and we do not go near the hotel the 'agent' suggested. Stay at another hotel." At 11.47am, there was another text message: "Monday arrival changed. You must not tell the coca-goons." At 12.16 pm, Frampton wrote: "WHY ARE YOU IGNORING ME? AT THIS LAST MOMENT. WE DID NOT DECIDE HOW TO MEET TOMORROW IN BRUSSELS AND KEEP COCA & LIVES. AT SIRU WE MAY LOSE BOTH!!" At 1.06pm: "We may do cool 1,000,000."

Frampton told the judges that these messages were jokes. He'd made them up because of Dixon's earlier warnings about drugs. "I was trying to keep Denise amused. I had already decided to fly back to North Carolina." But even taking his peculiar brand of humour into account, it was hard to understand why he would have taken the joke so far. He sent 30 messages of this nature, with specific details that made it seem as if he were referring to a real situation, a considered plan, not fabricating a story on the spot. Or did he think that whoever was behind the man who came to the hotel with the suitcase might hurt Milani if he didn't agree to take the bag? While for much of his life Frampton seems to have had little interest in money, he may well have seen his actions as a strategy to prove to Milani once and for all that he was indeed the husband of her dreams – a knight slaying dragons.

The defence worked to show that, far from hatching some elaborate plot, Frampton was unconcerned about the contents of the bag. Footage from airport security cameras showed him getting up from a cafe table and wandering off, leaving his open laptop and his two bags – his own white one and Milani's black one – unattended for up to 25 minutes at a time, gazing in shop windows, talking to security personnel, standing at an airline counter, returning to his abandoned luggage and then, an hour or so later, repeating the operation. Would anyone, even a wacky scientist, behave this way if he knew he was transporting 2kg of cocaine?

And if Frampton's behaviour was innocent, it still called for an explanation. Who leaves his bags unattended in an airport? Frampton, apparently. "I've seen him in airports," his ex-wife said. "He leaves all his bags and goes [off] for half an hour."

The prosecution continued to press its case, producing a piece of paper on which Frampton had written: "1 gram 200 dollars. 2,000 grams 400,000 dollars." The amount of cocaine found in the bag Frampton was carrying was 1,980g. When asked why he'd made this calculation, Frampton said, "My mind works in a strange way." That evening, Frampton told me on the phone, "I made those calculations in the airport office, after having been arrested", a fact that his defence team stressed the following day, noting Frampton's tendency to make random calculations. They asked him to explain another notation on the same piece of paper that read "5 standard deviations 99.99994%". Frampton explained: "The criterion for the discovery of the Higgs boson had to be 5 standard deviations, which means it's extremely unlikely to be a statistical fluctuation." He was "calculating the probability that Denise Milani would become my second wife, which was almost a certainty." Pursuing this line of questioning, his lawyer asked whether Frampton was also calculating the weight of one of the judges. "I'm embarrassed to admit it, but yes," Frampton answered. "I calculated that he must weigh 100 kilos."

"You calculated badly, as badly as you did about your second marriage," the judge responded. "I'm 124 kilos."

On the third and last day of the trial, the defence exhibited love letters Frampton had written to Milani, recovered from his email account. They were full of tenderness, vividly imagining their life together in North Carolina. She wouldn't need to work at first – she could accompany him to the office, make friends at the gym, the cafeteria and the supermarket; they'd take walks on the beach, and soon their baby would arrive. Eventually she could get a contract with Victoria's Secret. A response from Milani exhibited matching tenderness: "You're the best thing that's happened in my cursed life." But the judges were apparently unmoved by these declarations of love. As Frampton's former defence lawyer said, "The only thing that matters as far as the law is concerned is whether Frampton knew there were drugs in the bag. Whether he did it for money or a woman doesn't matter."

On 19 November, Frampton was sentenced to four years and eight months for drug smuggling.After the trial, Frampton said his lawyers had forbidden him to speak to me, fearing that he might say something "stupid". But three weeks later, this injunction was lifted and I went to visit him at the Czerniawskis', where he remains under house arrest. With credit for the time he has already spent in custody, Frampton is expected to be released in May 2014. (Under Argentine law, a foreigner must serve half their sentence and can then be expelled from the country and the penalty considered discharged.) It was a hot summer's day and he was dressed casually in a light blue polo shirt, white shorts, black socks and black trainers. He was still insisting on his innocence, but a new wariness had crept into his manner. He asked me several questions about myself, as if trying to gauge with each word which version of Paul Frampton I believed. He reported that the university would not make any decisions about his position until it had heard the results of his appeal, which could be months away. (The university confirmed that he still has his position, but that his current salary is $0.) His lawyers were using the same strategy they had before, but introducing further evidence, such as the complete record of his Yahoo Messenger chats with Milani, which he felt sure would exonerate him. "It shows unambiguously," he said later, "that the only reason I went to South America was to meet Denise Milani." For his part, Frampton had been working on two papers simultaneously: "So I can rest assured that I'm not like Oscar Wilde." While in Devoto, he checked out a copy of Oscar Wilde's Picture Of Dorian Gray from the prison library, and read in the preface that after Wilde's stay in prison, he gave up writing. "That really affected me. He lost his confidence."

The night before, Frampton told me, he watched the Nobel prize ceremony live from Stockholm. He described how the king of Sweden presented the prizes in a concert hall, adding that he had once been there himself. His greatest dream was "to have a prediction verified by experimentation". This, he said, was how you win the Nobel as a theoretical particle physicist. "That would bring an enormous sense of fulfillment, quite apart from the prize: 'I predicted a particle that's actually in the universe.' Wouldn't that be a rush? Much better than other ways of getting a lot of dopamine." Later, he reflected, "I've written 450 papers, an absurd number – a typical professor writes 100 in his career. I don't regret my work in physics, but I have made sacrifices." When asked what kind of sacrifices, he responded as if the answer were obvious: "Well, I don't have a family."

One of Frampton's last emails to Milani was written on a pirated phone a month into his stay in Devoto: "I only think of cuddling all day and having sex all night with Denise Milani. How can you prove that you are Denise Milani?"

• Maxine Swann is the author of the novels The Foreigners and Flower Children.

A version of this article first appeared in the New York Times.