He has spent the last year in Iraq's notorious Abu Ghraib prison, a suspected foreign militant many miles from home.
She remains in the neighborhood on the northeastern edge of Paris where they grew up, worrying, wondering, trying to bring him back.
But the 23-year-olds are separated by more than distance and prison walls.
He's a Muslim who grew up in a housing project and worked as a deliveryman. She's a middle-class university student from a Jewish background who has relatives in Israel.
Yet they fell in love. And they stayed together after he fell into the harsh world of Islamic extremism. He became remote, obsessive, groggy from overnight prayer rituals. He told her it was a sin for them to touch each other. So he sat across the room when she visited, making his mother serve as chaperone.
She remained loyal even after he turned up in Iraq, after 10 of his friends were slain, maimed or jailed, the human debris of a doomed odyssey. She still talks about their romance as if it has a future.
On one level, the story of Peter Cherif and his girlfriend is a Romeo and Juliet tale. On another, it offers a look at the confused world of young European extremists, for whom holy war can be as much about identity and machismo as religion, as much about group psychology as ideology.
"He was never anti-American," says the tanned, pretty student with long hair, her eyes shining with tears. "He likes McDonald's, rap, American war movies. He never said anything anti-Jewish."
The girlfriend asked that her name be withheld for reasons of safety and because she has kept the relationship a secret from her family. During an interview at a cafe here, the strain on her was evident. She toyed with her drink and fidgeted. The sound of passing sirens made her grimace.
"We talked a lot about Israel and the Palestinians, how kids and innocent people always suffered," she recalled. "He was more concerned about the Palestinians, so I told him about the Israeli side. And he listened to me. I can't believe he went off to Iraq to kill anyone."
But French anti-terrorism police say Cherif belonged to a cell of young Islamic extremists that took root in the 19th arrondissement of Paris in 2003. The youngest, Salah, was only 13 when he went off to study at a Koranic school in Syria. He allegedly helped operatives acquire weapons and cross into Iraq. Salah, whose last name is being withheld because he is a minor, has since disappeared.
Cherif was the sole member of the group with military experience. The others "trained" by jogging in Buttes-Chaumont Park, a lush expanse of rocky hills and waterfalls near their homes. In some cases, their determination seemed to waver: During the months when he was girding for combat in Iraq, one suspect also applied for a job with the Paris subway system.
Recruits to Islamic extremism are younger and more volatile today because radicalization happens faster than ever, investigators say.
"That's what's interesting and worrisome," a senior French anti-terrorism official said. "No logic, totally aberrant behavior. We've seen some of them, just before leaving for jihad, whose lives were dissolute, not at all Islamic."
Cherif's father, who died when his son was 14, was a Catholic Afro-Caribbean immigrant. His mother, Myriam, was born in Tunisia. She talks proudly about her own father's medal-winning exploits with the French military in World War II and Indochina. Myriam Cherif is a petite woman with flowing dark hair who has struggled with illness as well as her son's ordeal. She did not raise Cherif as a practicing Muslim; he did not speak Arabic as a child. His interests were typical: sports, MP3s, the Internet. He grew up in a household that cherished French values of democracy, secularism and tolerance, his mother said.
"I am not anti-American, I am not anti-Semitic. And there you have it: Peter's fiancee is Jewish," said Myriam Cherif, who has developed a warm bond with her son's girlfriend.
Their neighborhood is multiethnic. In drab public housing towers, working-class Muslim families predominate. Around the park and the scenic La Villette canal, gentrified pockets are spreading. The area has a significant Jewish population.
Cherif's girlfriend is not devout. One of her parents is Jewish; she regards Judaism as a strong element of her identity. She has visited relatives in Israel. She considers herself open to all faiths and nationalities.
"I have always had many religions around me, and I like it like that," she said.
France's immigrant neighborhoods can be hostile turf for Jews. Arson and vandalism against synagogues escalate when conflict flares in the Middle East. Orthodox Jewish men and boys often wear baseball caps to conceal their yarmulkes because of periodic assaults.
Nonetheless, Cherif's girlfriend says she has never had problems in her neighborhood, even during visits to Cherif's apartment complex.
"The project can be a little uneasy, but people have gotten to know me there," she said. "Everybody knows Peter; he's lived there since he was little. They associate me with him, and with his mother, and they leave me alone."
Part of the young woman's family migrated to France from an Arab country, like many French Jews. That shared background sometimes helps bridge the gulf with North African Muslims here. Despite ideological and religious tensions, some Jews and Muslims in mixed areas accept each other as part of a close-knit culture that treats neighbors differently than outsiders.
The couple have known each other since middle school, but their romance began in 2002 after they ran into each other on the street. Cherif had just been discharged from the army. He had permanently damaged his back and ankle in a parachute jump, ending his hope of joining an elite unit and following a military career like his grandfather.
Although hobbled, Cherif was athletic and broad-shouldered, and had a streetwise charm. As they grew close, his girlfriend said she began to see the world through his eyes. Like many dark-skinned working-class youths, he was haunted by prejudice and paranoia, by the conviction that his fellow French citizens saw him as a thug.
"He told me, 'You watch. You'll see how people react when we go out. They are thinking: What's a girl like that doing with a guy like him?' It was true. When people saw him on the subway, they would hide their cellphones like they thought he was going to steal them. That hurt him a lot. But he learned to live with it. He was proud to be with me. And I was proud to be with him," she said.
The relationship seemed to give Cherif a renewed sense of purpose. He got a job as a deliveryman, saving enough to buy a car and help his mother with household expenses.
"He was becoming a respectable, responsible guy," his girlfriend said.
But Cherif also turned increasingly religious, perhaps because of restlessness and the psychological blow of his career-ending injury. Anti-terrorism investigators say such traumas often open the door to radicalization.
Cherif started praying in his room every night, his girlfriend said, then decided to go to the neighborhood mosque. There he met Farid Benyettou. Only a year older, Benyettou wore thick glasses and unruly long hair beneath a turban, and had the magnetism of a true believer. His brother-in-law had done time for involvement in an Algerian terrorist network.
Cherif joined a "study group" that spent hours at Benyettou's apartment reading the Koran, praying and talking about Islam. The girlfriend said she never met Benyettou, whom Cherif called "my professor." But the street ideologue soon intruded into her life.
"It was like a sect," she said. "Benyettou knew all the weak and strong points of his disciples. He made them fast. He kept them awake all night praying. The fatigue made them vulnerable. Then he started clearing the environment around them. He knew I was a strong influence. He told Peter to get rid of me; I was an obstacle to his faith, a non-Muslim."
Cherif acquired a beard and a withdrawn, sullen air. He recoiled from sexual temptation, avoiding physical contact with his girlfriend and even averting his eyes from billboard advertisements for lingerie.
But unlike other wives and girlfriends of European extremists, she never considered converting to Islam. She thought she could eventually rescue him from fanaticism. Despite the tension and bickering, she was encouraged that Cherif seemed unwilling to break up with her. So she accepted Cherif's insistence on a purely "spiritual relationship."
"We talked a lot," she said with a melancholy grin. "We couldn't do anything else, so we had long conversations."
Cherif's transformation also distressed his mother. She passionately denounces radical recruiters such as Benyettou, who was jailed here last year on charges of sending his disciples to fight in Iraq.
"They toy with our children, brainwash them," she said. "They bring together a group and tell them they are all brothers together. That fraternal love, it fulfills something everyone is looking for. But it turns into hate for the outside world."
In early 2004, Cherif took part in protests against a French law banning Islamic head scarves in public schools. He was filmed by news crews and police intelligence officers next to Benyettou, raging against France and praying on the sidewalk.
Investigators say Cherif's group also displayed the fierce anti-Semitism common among Islamic extremists. One suspect made threatening comments about taking revenge on the Jewish owner of a restaurant where he had worked, according to investigators.
Cherif opposed the war in Iraq, his girlfriend said, but so did she.
When he left for Damascus, the Syrian capital, in May 2004, he said he was going to join friends studying at a Koranic school. The school has served as a way station for European jihadis on their way to Iraq.
Back in Paris, Cherif's mother and girlfriend were not enthusiastic, but at first the experience seemed positive. Cherif communicated almost every day with his mother using a webcam at a cyber cafe, and his girlfriend often came to her house to take part.
"He said no one looked at him strangely on the street in Syria; he felt welcome, comfortable. He told his mother we should come visit. It's hard for me to think he was getting ready to fight in Iraq if he wanted us to join him," his girlfriend said.
But by July, Cherif had cut off contact. His girlfriend heard his voice for the last time during a short, tense call to her cellphone in November 2004. Cherif asked insistently about his mother. He told his girlfriend not to use his name on the phone.
"He told me: 'I can't talk right now. I'll try to call you again, but I can't promise anything.' Then he hung up. I looked at the number and I realized it was an Iraqi area code. From then on, I was desperate," she said.
U.S. troops in Iraq captured Cherif and another Frenchman near Fallouja on Dec. 2, 2004, shortly after the ferocious battle for that insurgent stronghold. Court documents indicate Cherif was detained, unarmed, at a checkpoint and imprisoned at Camp Bucca in southern Iraq. In August 2005, he was transferred to Abu Ghraib.
At least three of his friends have died in combat or suicide attacks in Iraq, French investigators say. Another, Mohammed Ayouni, turned up recently in Syria missing an eye and part of an arm. Syria deported him to France, where he is in jail on terrorism charges. Ayouni sustained the wounds fighting in Fallouja, the senior official said. Ayouni says he was helping rescue civilians caught up in the fighting, according to his lawyers. Three more suspects are jailed here.
Although the fate of his friends does not help Cherif's case, his girlfriend and mother question the length of time he has been held and the fairness of Iraq's judicial system. In March, lawyers acting on behalf of Cherif and the two women filed suit here alleging unjust imprisonment.
"We believe the length of time he has been held and the lack of information about the charges are violations of international law," said Olivier Foks, one of the lawyers. "After 19 months in this situation, our goal is that he be repatriated to France and that the French justice system looks into his case."
Communications are very limited, but Myriam Cherif says the International Red Cross has delivered three brief messages from her son. He is apparently in good health. He has been housed in a large, air-conditioned tent where inmates can watch DVDs, Foks said.
In response to a recent inquiry from the Los Angeles Times, a U.S. military spokesman in Baghdad reported that Cherif was tried in Iraq's Central Criminal Court between June 28 and July 4 on charges of illegally crossing the border. Iraqi courts sometimes use immigration laws to go after suspected foreign fighters.
Cherif was convicted and will be turned over to the Iraqi prison system, said Army Lt. Col. Keir-Kevin Curry, the U.S. military spokesman. The sentence: 15 years.
Cherif's girlfriend wants to believe that he did not take part in combat.
"It's possible he was convinced to fight, but I want to think he hung onto his true ideas," she said. "I hope he gets brought back to France. He has to explain himself to everyone. He has to explain himself to me."