TAMPA — Addison Allen was 16, about to start her senior year at Tampa's Robinson High School, when the police called. They wanted to talk about the rumors.

Several students had said she was having sex with her European History teacher. One told an officer he'd seen text messages between the two and they'd gone on a date to see The Avengers at WestShore Plaza.

Impossible, thought Lynn Allen, Addison's mother, as the officer stood near their dining table that summer day in 2012. They'd seen the movie as a family.

"So nothing happened?" the mother asked her daughter.

"No," Addison said and walked upstairs to her bedroom.

The officer left. Her mother and father went into her room. After a long silence, Lynn asked her husband to leave. She looked hard at her daughter.

"It's all true," Lynn said, "isn't it?"

• • •

Addison struggled to make friends her freshman year. Something changed when she was a sophomore, the year she took Robert Lunsford's advanced placement history class. She hosted tea parties at her South Tampa home, invited friends over to play Scrabble, dated a boy.

She also nurtured a crush. She filled her diary with hearts and teenage fantasies, and often signed off as "Addie Lunsford." "I know it will never happen but a girl can wish, can't she?"

Her mother welcomed the changes. She listened to her daughter debrief her each day after school. The highlights were often funny things Lunsford had said in class.

Lunsford, then 37, was the cool teacher. In the summers he took recent Robinson High graduates to Europe, where they'd see the sights they'd studied in class. He asked parents to sign waivers to allow their kids to drink alcohol. (The legal drinking age in many European countries is 18.) His guide company was called DYNOtours: "Deny yourself nothing!"

At the end of sophomore year, Addison said, Lunsford asked her to help him grade papers after school. They exchanged phone numbers and started to text each other.

In her junior year, she became Lunsford's teaching assistant. On Tuesdays, she said, the two would grade papers and joke until 6, even 7. It was her favorite day of the week.

Her mom told her not to stay so long. But Lynn, 48, remembered volunteering as her high school's football team manager to be near a cute coach. She didn't see any harm in her daughter's crush. Addison seemed more outgoing and happier than ever.

In the spring of 2012, Lunsford coached a girls tennis club, and Addison's Tuesdays alone with him ended. One Friday, she said, she stopped by his classroom. The movie The Avengers came up in conversation. It was so good, Addison said he told her, he'd even see it again. Almost jokingly, she asked if he'd see it with her.

He agreed.

They met at the mall theater and shared popcorn. She said she dropped a piece on his lap and he playfully threw it back. In the movie, Captain America knocks a punching bag off its chain. Addison said Lunsford leaned near and joked, "I hate when that happens."

She laughed so hard.

They hugged in the parking lot, Addison said, and decided they weren't ready to say goodbye. They sat in his car and talked for nearly an hour. The conversation, she said, turned to sex.

"Would it be your first time?" she said he asked.

"Yes."

He said he was intrigued.

They began to meet covertly, she said. Hugging turned to kissing and eventually more. She said they met in a Sonic restaurant parking lot on Gandy Boulevard and twice at his house while his wife was away.

Then Lunsford left for Paris with a group of recent graduates.

They planned to meet July 5 after he returned. Addison decided that would be the day. In her diary, she wrote a reminder to her future self: "July 5th is a significant date. I hope you remember why."

She didn't immediately follow up with an entry about the experience but eventually noted it was "really nice."

She said they had sex four times. She'd meet Lunsford at a nearby bank parking garage and ride with him in his car to his house. His wife, who was pregnant at the time, was at work, and their child was in day care.

Addison's happiness was hard to contain, and she told friends.

At the end of July, one of them called police.

• • •

Addison said she didn't want anything bad to happen to Lunsford, so she lied to investigators.

When her mother sat next to her that night on the bed and learned the truth, she persuaded Addison to at least tell police she had seen the movie with Lunsford. That way, Lynn said, the Hillsborough County School District would move forward with its investigation and he wouldn't be able to teach anymore.

The police talked with Addison's friends. They interviewed Lunsford, who insisted the two had never had sex and that Addison was obsessed with him.

Lunsford resigned Aug. 14, 2012, about two weeks before the start of school. He told people he planned to focus on his travel company.

Lynn, a family therapist, and her husband, Tim, mulled options. They could press Addison to cooperate with police, but what repercussions would that have on her senior year, and as a result, her college years? Would the public exposure from the case deepen her already depressive moods?

At the time, Lynn didn't think Lunsford was a pedophile, only that he had "poor boundaries." She worried how his children would turn out with a registered sex offender as a father. At the same time, she wanted to prevent him from working with teenage girls.

She concocted a solution she hoped would be best for all.

On Sept. 2, 2012, she sent Lunsford an email:

"I've been debating writing you … there are only two events that would lead me/us to ever decide to dredge this thing up again. One would be your reconnecting with Addie … and the other would be if I found out you were working with 12-17 year old girls again."

He responded the next day.

"Thank you for your email. I am sorry for the pain this has caused both our families, and I welcome the opportunity to reach an understanding so that we may all put this behind us … In short, you have my solemn promise that I will honor both the letter and the spirit of your two conditions … I am so deeply sorry for this. I do not believe that my behavior reflects the person I truly am, and certainly not the person that I am trying to be … Thank you, Rob."

Earlier, Addison had sent an email of her own.

"I love you so much, and I'm just so sorry."

Lunsford replied:

"Delete all the messages and get rid of anything else you have that is a reminder of this. It will just provide the temptation to revisit it. The best thing for everyone, but especially you, is to move ahead."

Addison stopped socializing. She heard the whispers as she walked the school hall. She felt guilty each time she passed Lunsford's former classroom.

Without her help, the Tampa Police Department's investigation hit a wall.

Meanwhile, the school cleaned out Lunsford's room and found a blue thumb drive. On it were two letters district officials believed were to a female former student. The letters were dated fall of 2010 and winter of 2011. They referred to a previous trip to Europe and to making "love under an Italian moon."

With the police's investigation stalled, officers would never see the letters. Because Lunsford had resigned, the school sent what it had collected to the state's Education Practices Commission.

• • •

Lynn believed she bore responsibility to ensure Lunsford followed through with his side of the deal.

She scoured his Facebook page to make sure no young girls repeatedly liked or commented on his photos, as Addison had. She drove past his house several times a week. If he got a new job, she thought, she could follow him.

She did this for a year.

One day in May 2013, without much thought, she pulled up to a stop sign near his house. Parked at the intersection on the other side was Lunsford's black Hyundai Sonata, she said. A young female sat beside him in the passenger seat, Lynn said, probably "between 16 to 21 years old." It was around noon. Lynn swung her car around, parked near Lunsford's house and watched him walk inside with the young woman.

Lynn sat in her car for more than an hour, she said, staring at the front door. The two finally emerged and drove away.

About 10 minutes later, she saw Lunsford driving home. His passenger seat was empty.

Lynn called her husband.

Then she drove home and called the police. This time Lynn shared everything with the officer. She recounted how Addison had lied and her email deal with Lunsford, and said she felt sick when she saw the girl in Lunsford's car. The officer took down Lynn's statement and asked a detective to follow up.

• • •

The detective reinterviewed everyone and filed a report to the State Attorney's Office in Addison's case.

Prosecutors chose not to charge Lunsford because of "delayed disclosure, no corroborating evidence and insufficient evidence," records state. Lynn said the detective told her a judge would have had a hard time trusting Addison because she had lied.

After a yearlong investigation, the Education Practices Commission sought to revoke Lunsford's teaching license.

The investigation report — more than 70 pages — included interviews with students, Addison's diary clippings and emails sent between Lunsford and Lynn. In February of this year, an administrative complaint said Lunsford had an "inappropriate physical relationship" with a student that included "sexual intercourse."

Lunsford chose not to contest the allegations and voluntarily surrendered his teaching license. In July, his Florida teaching permit was permanently revoked.

In a recent interview with the Tampa Bay Times, Lunsford said Addison and her mother lied about everything. The allegations stem from Addison's unhealthy obsession with him, he said. He resigned his job and wrote emails of apology, he said, because he felt bad that the rumors had spread. He accused Addison of signing him up for spam emails and said she recently left a note on his car.

Concerning the letters found on the blue thumb drive, Lunsford said, "Even if that was the case, hypothetically, that wasn't a crime," referring to the girl's age.

Addison is now 19. She is a sophomore and studies political science at New College of Florida in Sarasota.

She admitted that she signed Lunsford up for child-abuse-prevention newsletters and that once when she saw his car parked in her parents' neighborhood, she left him a mean note. She also said she sent him an email this summer. She wanted him to know that his actions caused her to feel severely depressed.

Sitting in a chair in her dorm room, she said that for a long time she struggled to see herself as a victim. But she has finally accepted the relationship for what it was.

"This was purposeful on his part," she said, "purposeful manipulation."

That realization has liberated her from blaming herself, and she has felt much happier recently.

Lately, another student her age has caught her interest. If it turns out to be something special, she'd like that, but for now she's fine being just friends.

Times researcher Natalie Watson contributed to this report. Contact Weston Phippen at wphippen@tampabay.com or (727) 893-8321.