A woman is attacked after being dropped home by her boyfriend, her clothes were shredded and her hair cut short. Olivia rides with her to the hospital while Elliot stays in the crime scene. CSU find some hidden cameras in the woman's home. Munch and Fin go in search of the peeping tom.
Olivia talks to Cassie, the cellist who was attacked, and tells her there's no sign of sexual assault, but this was definitely a sexual motivated attack. Elliot interviews the boyfriend, and he says that the Orchestra conductor is the one they should look at. He's been after her and even lended his apartment to her. He becomes a suspect of having planted the cameras.
Elliot and Olivia talk to an ex-girlfriend of him, who was a violinist in the Orchestra before Cassie. She tells them she broke off the relationship because she discovered tapes of her and other girls before her in his closet.
Fin and Munch trace the filming gear to a deceased man. ADA Cabot says they don't have enough probable cause to search Robert Prescott's apartment. The guys pressure her for a way to search his house, since he must've taped the attack, and she manages to get a warrant. They search the place and find a big collection of secret tapes of him and many different girls, even Cassie. Olivia and Elliot suspect Cassie is hiding something from them and confront her.
She tells them she ended the affair after she caught him in bed with another girl, but he showed her the tapes of them and blackmailed her into staying in the Orchestra. She says he have been calling and leaving flowers to her ever since.
Robert Prescott goes to the department with his lawyer to give a statement. Olivia and Elliot interview him, and while they are at it, another attack happens. Elliot rushes over and Munch and Fin show him a broken cello with a message that reads "die bitch".
Mr. Prescott is cleared as a suspect and they start thinking it may be a disturbed fan. They trace the date of purchase of the filming gear and investigate who had access to Cassie's apartment during that time. The doorman of the building gives the police the name of a security technician that was in her apartment at that time.
The manager of the security tech company tells Elliot that Ray Campbell, the man he's looking for is a model employee, and has been working for him a long time. But when he checks, he finds out that he was supposed to be in another location on the day he went to do maintenance in Cassie's apartment. Elliot goes talk to Ray and is informed that he had his uniform, tools and his employee number stolen, and the signature on the maintenance invoice for Cassie's apartment is not his.
They find another address where Ray's signature was also forged to install a DSL connection, and figure it is where the stalker was sending the images from Cassie's apartment. They find the website where the images are being hosted and there is only one IP accessing it.
Elliot, Olivia, Munch and Fin go to Terry Willard's apartment. He isn't home, but they find a shrine he made for Cassie, with pictures, flowers and things he took from her. His girlfriend tells them he works in a webdesing place, but when they check, they find out he was fired a few months back. His former boss explains he was distracted and missing days of work before being fired and turned violent when he was finally let go.
Captain Cragen calls Cassie to the precinct, they show her a picture of Terry and tell her he's been stalking her since she was in college. She doesn't remember him from college or anywhere else. They ask Cassie's help to get him, she has to send a message to him in her next performance, so maybe he will try to talk to her and they can catch him.
They set a face recognition program and stop a few suspects, but none of them turn out to be Terry. A crew member finds a box with flowers and a dead rat in Cassie's dressing room. The facial recognition finally gets the right guy and they arrest Terry. Elliot interviews him with captain Cragen, but he swears he wasn't the one who attacked her.
A few hours later Terry's girlfriend, Amy bails him out. Meanwhile Captain Cragen announces Cassie's been shot. Eliot goes to track Terry down, while Olivia stays in the hospital waiting for Cassie to wake up.
Munch and Fin go to talk to Amy, she says she didn't see Terry and takes off in a cab. Fin and Munch follow her to a hotel room. Olivia and Elliot go there and the four of them break the door down. She confesses to attacking Cassie both times, Elliot finds Terry dead in the bathroom.