Benson and Stabler meet Warner at the scene of a dead body. Benson notes the victim looks like a kid, but Warner shows the girl's ID, which states she's 23. The victim also has defense wounds and was anally raped. Another disturbing note is that nearby residents all confess they had heard a girl screaming, but nobody left their apartment to investigate.
The victim's ID is a phony. Fin investigates recent missing persons cases and comes across their victim, 17-year-old Anna McWilliams. Anna's father identifies the body and tells the detectives of how Anna just lost her mother to cancer and went through a change, including dumping her long-time boyfriend, Henry. Benson and Stabler immediately head to the high school to question Anna's ex.
Henry tells the detectives he went out with Anna that night, but she quickly ended their date to answer a text from the mobile web site, "Anonymous Quickie," where people can find strangers to hook-up with for sex. The SVU are able to identify her last hook-up, Peter, and arrest him for Anna's rape and murder.
After searching Peter's social networking site, they find he's friends with a past rape victim whom the SVU interviewed years before, Rebecca Ellison. Benson pays Rebecca a visit. She confirms she had a one-night stand with Peter before her rape and he was rough during their time together, but a recent DNA test clears Peter of her attack, as well as Anna's. Stabler questions Henry again, and he confesses to Anna's murder.
After solving Anna's murder, Warner comes in with more damaging news. Anna was HIV positive at the time of her death and her last sex partner, Peter, was positive, too. Benson and Stabler know about Peter's very promiscuous lifestyle and now worry they've released a potential serial killer. They pay Peter a visit, who confirms he's HIV-positive and admits to having unprotected sex with the women he meets online.
Benson and Cabot pay Rebecca visit, where she admits she is HIV positive and she begins to suspect it was Peter who infected her. Cabot encourages Rebecca to testify against Peter in order to help put a stop to his passing of the virus. Rebecca agrees to help.
Benson returns to the SVU to pay Peter a visit. He continues to show no remorse for spreading his disease. When Benson begins to pry about Peter's relationship with his mother, he spits at her and tells her his grandfather is the only man who ever gave a damn.
The trial begins for Peter and Warner gives damaging testimony against the defense. Chaos breaks out in the courtroom when Rebecca charges in and sprays Peter with sulfuric acid. Benson, Cabot, and Stabler head to the hospital and find out just how extensive Peter's injuries are.
Peter's lawyer alerts Cabot that he's suing the DA's office for negligence in not protecting his client from Rebecca's attack and he'll drop all charges if Peter's charges are dropped, as well. Cabot visits Rebecca in jail and recommends she take a plea for her assault on Peter but Rebecca refuses. Cabot has no choice but to try Rebecca's case.
During Rebecca's testimony at her trial, Cabot is forced to bring the claws out. Cabot makes Rebecca admit that she should have known better than to have unprotected sex with Peter and shows the jury a photo of the giant AIDS awareness billboard outside Rebecca's apartment, proving that Rebecca's own negligence caused her condition.
After the painful testimony, Dewey Butler, Peter's grandfather, pays Cabot a visit. He tells Cabot he wants to take the stand and defend Rebecca for her maiming of his grandson. Cabot tells Dewey that she cannot let him do that and he leaves. Dewey tells Benson and Stabler he tried to warn Rebecca and all the other girls Peter slept with. The detectives are left confused about what Dewey means.
Stabler and Benson head to the Butler residence to ask Dewey more about the "warning" he gave all of Peter's lovers. Peter answers the door and tells the detectives his grandfather doesn't want to see them. In return, Stabler and Benson drop a bombshell on Peter, telling him it was Dewey who alerted Peter's FaceUnion friends and the media about Peter having AIDS. Peter is shocked and confronts his grandfather.
Stabler and Benson watch as Peter asks his grandfather why he did what he did. Dewey tells Peter the truth about Peter's mother and how she killed her abusive boyfriend when Peter was very young and she ended up dying in prison. Dewey thought this whole time he was doing the best thing by telling Peter he was abandoned instead.
Dewey admits he thought he was doing right by keeping the truth from Peter, but in the end, he did a terrible job raising him. Dewey then collapses in Peter's arms as Benson grabs a bottle of empty sleeping pills from his hand. Stabler calls for an ambulance as Peter sobs. Dewey's last words are to tell his grandson to become a good human being.
Peter takes the advice of his grandfather and tells Cabot he'll plead guilty on all counts he's charged with. Rebecca's charges have been dropped, as well. Before passing away, Dewey had also signed away all of his inheritance to go to the women Peter infected with AIDS.