Morales reports that AQ helps people hook up by using cell phone GPS signals. Morales demonstrates the service then shows the detectives that Anna spoke to a user named BigPeter last night. Olivia poses as a person wanting a quickie and has BigPeter meet her. Fin arrives and arrests BigPeter for the rape and murder of Anna.

At the station, Peter says he didn't kill Anna. Peter says he is on AQ since he doesn't have time for dating.

Morales looks at Peter's phone and finds a woman named Rebecca Ellison who is connected to one of his social networking profiles was raped two years ago.

Olivia visits Rebecca and asks her to recall what happened during her attack. Rebecca says the attack happened quickly and she blacked out. She says she met Peter at a party and had a one night stand with him. Rebecca remembers Peter was violent during sex. Warner compares Peter's DNA to the one in Rebecca's rape kit and sees that it doesn't match. Warner compares Peter's fingerprints to the prints on Anna's neck and sees it also doesn't match. She figures that the killer was young or never worked in his life.

Elliot and Olivia meet with Henry's mother and shows her a warrant to obtain his prints. They go into his room and finds him hiding in a closet. At the station, Elliot tells Henry they found his prints match the killer's. Henry says he followed Anna to the park, watched her having sex with Peter, and confronted her. Henry says Anna told her she never loved him and asked him to leave her alone.

Warner reports that the semen found on Anna was found positive for HIV. They see that the semen belonged to Peter.