To step off a busy northwest London thoroughfare into Richard Ratcliffe’s flat feels like passing through the wardrobe into the dark horror of a fairy tale. Three months ago, he was an ordinary middle-class accountant, living with his wife and their nearly two-year-old daughter, “muttering about the commute, going to take out the bins, clearing up those toys again. You know, all that sort of stuff.”

Now, the nursery sits empty, and all that remains of his 37-year-old wife and daughter are their faces smiling out of photographs. Ratcliffe, 41, last saw them as he waved the pair off on a holiday to visit family in Iran. When he will see them again, nobody knows.

Eighty-three days have now passed since his wife was taken , yet he maintains a veneer of calm self-possession. Composed and softly spoken – even when he swears, it is with the gentle, this-just-isn’t-cricket bemusement of a mild-mannered Brit. Occasionally, the narrative becomes chronologically muddled, but I can’t work out whether he is self-censoring, for fear of saying anything that might make the situation worse, or so frayed by sleep-deprivation that the days have blurred. Or perhaps it is only because the story is so fundamentally senseless – an Alice in Wonderland rabbit hole of Kafkaesque nightmares – that, as he says, “there is no truth there to get to the bottom of”.

Ratcliffe met Nazanin Zaghari through a friend in November 2007, two months after she arrived in London to study a masters in communication. Ratcliffe was half an hour late for their first date, at the National Theatre’s coffee shop, “and the first thing she did when I got there was she punched me on the arm. I thought, ‘That’s quite a good sign,’ he grins. “We just clicked.”

Nazanin Zaghari, Richard Ratcliffe and their daughter, Gabriella, aged 22 months. Photograph: AFP/Getty Images

Her Iranian citizenship represented nothing more problematic to the couple than the mild absurdities of bureaucratic inconvenience. The Home Office declined her parents permission to attend the couple’s 2009 wedding in Hampshire, but “we had a number of them, actually,” Ratcliffe says – they married again in a London mosque.

Following a third, Iranian-style marriage attended by her family, and after much hilarity over the UK’s “ridiculous” citizenship test, she was granted dual-nationality status. During family visits to Tehran, Ratcliffe had sensed no ominous undercurrents, and in March, his wife took their daughter, Gabriella, home for another unremarkable holiday.

When his brother-in-law called him to say she had not boarded her flight back to the UK due to a problem with her passport, and had been taken for questions, he told Ratcliffe not to worry. “And I didn’t. Stuff happens in Iran, you know.” He went to work as normal that day, and the next, unaware that his in-laws were “an awful lot more worried than they let on to me. Now I think, as a rule,” he offers drily, “if anyone in Iran tells you not to worry, do the exact opposite.”

Officials confiscated Gabriella’s passport and handed her over to her grandparents. Three days later, Mrs Zaghari-Ratcliffe phoned her family from the airport and texted her husband to say “It’s all over, all finished.” It was a Wednesday, and she would be released on Saturday once the necessary official signed her out. “At that point I got cross. I thought, ‘You fuckers,’ – you know – ‘bloody public sector, the official’s just gone home because, of course, their weekend is Thursday and Friday. I just thought: ‘This is a bit shit.’”

When she wasn’t released, but transferred to a prison 1,000km away, still Ratcliffe went to work and told nobody except his parents and his wife’s boss. She works for the charitable foundation arm of Thomson Reuters, which contacted the Foreign Office. Ratcliffe approached the Red Cross and Amnesty International, but told no friends. “It’s almost like a denial mechanism, isn’t it?”

Everything changed when news came that she was being held by the Revolutionary Guard. “That means spy. In a good case, with no charges, she’s out in three or six months. Otherwise it’s 10, 20 years, death penalty.”

The Zaghari-Ratcliffe family. Photograph: Facebook

Ratcliffe spoke to former Iranian detainees, who told him she would be held in solitary confinement, under constant interrogation, pressured to sign a false confession. “They had horrendous stories, really properly horrible ones. And that’s when I realised I’d left my wife going through that without realising. For me, that was the hardest moment. I sat there thinking, what have I done?”

Worse than guilt, what he felt was shame. Both the Foreign and Commonwealth Office (FCO) and her family had advised him to keep quiet, but “still you think: I should have tried to protect her. Ultimately, I hadn’t done that. And she’s my wife. I felt negligent. I hadn’t done everything I could to try and rush around and understand things more quickly.”

Ratcliffe faced the hardest decision of his life. “To a person, all the families of former detainees told me: ‘I wish we’d gone public earlier.’” But his father-in-law was horrified by the idea, fearful of provoking retribution. Ratcliffe stopped sleeping, couldn’t eat, and almost “fell apart”. When he informed the FCO of his intention “they shat themselves” and tried to talk him out of it. “I got quite a lot of advice from various experts to be careful of Iranian sensitivities. ‘They’re very sensitive, don’t try and offend them.’ Fuck that, it’s not that sensitive.” With just the help of a couple of old friends, on day 36 of Nazanin’s captivity, he issued a press release and opened an online petition for her release.

It seemed to work. Three days later, his wife was removed from solitary confinement and taken to a hotel for a family visit with Gabriella and her parents. “At that point she couldn’t stand, she was terribly weak, she had to have Gabriella lifted on to her. She couldn’t walk without blackouts, her hair was falling out. What they do is a very nasty psychological process to break your spirit. I don’t think there’s anyone whacking her with a stick or anything – we’ll never know until she’s out – but she was clearly very, very traumatised.” She was returned to prison, but no longer in solitary confinement; within 10 days, the petition had half a million signatures, and on 5 June, she phoned her family to say “It’s all finished. I’m being released without charge.”

A few hours later, another call came, from the Revolutionary Guard. “They said there’s been a mistake. She’s not being released. And then she went quiet. She disappeared.”

For a while, even her family stopped calling him. He subsequently discovered that the Revolutionary Guard had threatened to take his brother- and sister-in-law too, if the family continued to contact him. In the vacuum, Ratcliffe has been left to try and make sense of the opaque mystery of Iran’s internal and foreign politics.

Since his wife was detained, two further dual-nationality citizens have been taken while visiting the country. “They’re clearly looking every month to find a foreigner to frame. And the more I understood, the darker it got.”

He doesn’t know if the broken promises to release her are a psychological device, or evidence of factional disagreements. “It’s not clear to what extent these detentions are a coherent strategy, or just hard-liners wanting to mess stuff up.”

Nazanin Zaghari and Richard Ratcliffe while she was pregnant with their daughter

Sometimes, he wonders if the Revolutionary Guard has genuinely mistaken his wife’s CV for evidence of espionage, even though the Thomson Reuters Foundation has no presence or operation in Iran.

“The [Iranian state] are paranoid, so maybe that’s made them suspicious.” Or perhaps, he then says, “they took Nazanin to understand more about the global NGO system”. But moments later he adds, “They know it’s all bullshit,” and wonders if “fundamentally, it’s a hostage situation. It could actually be just a money-making racket.”

One category of prisoner can be bought back for £50-200,000, he understands, and released quietly. “We could sell our flat, and it would be OK. But if it’s a full-on espionage charge, and they are keeping her as hostage collateral for a deal with the British government, I could ask the entire block to sell up and you wouldn’t have enough money. It’s really big money, like proper government-spending-level money.”

The news last week was bad. Zaghari’s case has been transferred to the revolutionary courts, and she has been returned to the capital in anticipation of being charged, according to state media reports, with “planning the overthrow of the Islamic regime in Iran”. She has still not been allowed access to a lawyer. When I ask if he has ever wondered whether she might conceivably have been leading a secret double life, he just laughs and shakes his head.

Ratcliffe did not meet with FCO officials until after he had made his wife’s case public, and then only at his request. “It felt almost like the FCO resented me for going public. I was angry, and I felt gamed. We would have a series of calls, and there would a sort of strange dynamic, where occasionally it felt like they were almost trying to get me on record as having said how helpful [they had been]. It’s like dealing with a fucking insurance company trying to get out of paying a claim. This is a really odd definition of support, isn’t it? It is a really odd dynamic to be covering your arse that early on.”

Ratcliffe describes the government’s position as: “‘This is a delicate matter, we’ll hope the Iranians will be nice.’ It’s like, ‘delicate’? I mean, if this was your wife … They can use political capital to force the situation. But there has been no public statement of criticism by a senior politician, and the Iranians notice that. The touchstone of it will be when the prime minister picks up the phone or makes a public statement. That’s when the Iranians will know that this is an issue people care about in Britain.” Until then, “they’re not that fussed”.

Meanwhile, “There’s a decision to make about Gabriella.” If his wife is granted bail before going to trial, he knows she will want to be with her daughter – and he also fears being arrested if he tries to go and bring her home. When she left, what few words she had were English, but by now she speaks Farsi to her father when he makes his nightly call by Skype – “and my Farsi’s not great”, he says.

Her attention span isn’t great either, he smiles. “But if we play peekaboo or I’ve got her little Peppa Pig, then she’s quite entertained.” The calls are “the best bit of my day”. He spent fathers’ day at the National Theatre coffee shop, to remind him of that first date. “I wanted just to be close to them there.”

Former hostages have warned him that “the hard part is not this part, but when they come home. I think it will be a very long journey back. Life-changing, for sure. He last spoke to his wife from prison in May, when she was briefly released from solitary confinement.

“She was pretty upset with me, for publicising the conditions she’d been held in. But I see my role as doing everything I can to point out how outrageous this is, and say the government should do something, and the government’s doing nothing.”

On Tuesday, he will hold a candlelit vigil outside Downing Street, and when the petition reaches 1m signatures, he will deliver it to the Iranian embassy.

Does he ever worry, I ask, that he should have kept quiet? He pauses to compose his features, and the strain in his eyes is unmistakable.

“All I can do is try and campaign and make noise and try and make other people concerned, to get the government concerned. Without information, you can’t galvanise public energy. And if enough people care, she’ll come home.”

The petition to free Nazanin Zaghari-Ratcliffe is online at change.org