A drycleaning shop finds a dead body in one of their machines and the SVU is called to investigate. Their victim is in her 20s, and appears to have been raped and tortured before having her throat slit. The delivery came from Mercy Hospital and Benson and Stabler question the driver responsible for picking up the laundry from there. Surveillance cameras catch a man dropping off the body in the truck while the driver was in the hospital.
The victim, Samantha Millerton, has an arrest record for protests. She worked for an environmental organization, CLEAN, and lately had been targeting the CEO of an oil company, Nicolas Turner. Stabler and Benson immediately pay Turner a visit. Turner has an alibi, but using surveillance footage from the company's headquarters, they see Samantha attempting to trespass, only to be attacked by an assailant and thrown in a car. The car is traced to Jason Gamble and they bring him in to the SVU.
Because Jason shot at Benson and Stabler while they were arresting him, Cragen gives the case to Fin to close. Jason has a box of items belonging to women, one of which is a bracelet of Samantha's. Jason swears to Fin he didn't kill Samantha and that's he's been a model parolee since spending some time in jail for embezzlement. His parole officer vouches for Jason's clean parole record. But he does admit Jason has been acting strange in recent weeks and he once found a door in his house that was padlocked.
The detectives dig through Jason's house and find a basement that's been used as a torture chamber. Police have managed to ID almost all of the articles found with Samantha's bracelet, only problem is they link to rape and murder victims from over 40 years ago - before Jason was even born. The detectives go to interview one of the rape victims whose engagement ring was found, only to discover she has Alzheimer's and being cared for by her daughter, Vivian.
Benson tells Vivian that she had found Joan's engagement ring from 40 years ago when it was taken from her. Vivian cannot believe that the police department remembers her mother's case from that long ago, but Benson is left with the difficult task of telling Vivian her mother was raped at that time, and that's how the ring was stolen. Vivian gets angry when she realizes she was the product of her mother being raped. She storms back inside her home.
Vivian's son tells Benson that he's worried his mom will turn to drugs again. Benson finds Vivian in a park taking pills and drinking beer. Benson tells Vivian she was the result of a rape too, and knows how hard it is to find out. Vivian says her mother always treated her like a burden and now she sees why, but she considers herself lucky to have a man she thought she was her real father, to grow up with and raise her with love. Benson begins asking more questions about Joan's rape.
Benson begins to think that Joan's rapist was the same man who raped her own mother, making her and Vivian half-sisters. She confides her suspicions in Huang and Stabler, who think Benson's theory is way off. Benson admits she grabbed a can out of Vivian's garbage to perform a DNA test to see. Stabler tells her that she's reaching on this theory of hers. Stabler also points out that there needs to be a connection between Jason and Joan's rapist explaining all the souvenirs that were found on him.
Benson and Stabler discover that Jason's cellmate while in prison was serial rapist by the name of Walter Burlock. Walter has just been released on parole and the detectives head to his favorite strip joint to ask him some questions. At the strip club, they discover Walter's tab is being paid for by Jason's credit card. This also explains why Jason was acting weird to his parole officer around the same time Walter was released from prison.
Jason's lawyer presents evidence showing all the sexual abuse Jason suffered with Walter as a cellmate. Out of this fear, Jason took Walter into his apartment when he was released on parole. Jason says he saw Walter bring Samantha down to the basement and murder her, and it was Walter who shot at Benson and Stabler when they came by the house originally. The new ADA Hardwick tells detectives she cannot arrest Walter because they didn't have a proper search warrant when they discovered the torture chamber.
Vivian's son escorts his stoned mother into the SVU. Stabler takes Calvin upstairs to the children's room so Benson can talk to Vivian alone. Benson tries to persuade Vivian to get treatment for her addictions, but all Vivian is concerned about is finding her real father. She tells Benson that her mother died the night before and she's just treating the rage she has with pills.
Vivian agrees to look into counseling and she and her son Calvin exit the squad room. As the two are in the hallway, a just-released Walter starts telling Calvin how corrupt cops are. Benson sees the interaction and flips out, telling Walter to walk away. Walter continues on about how Benson thought he was a rapist based on souvenirs found in an apartment and Vivian puts it all together that Walter is the man accused of raping her mother and may be her father. Vivian lunges at Walter before Benson tears her away.
Benson and Stabler have a stakeout on Jason's home and know that Walter has returned there since being released from prison. They watch Jason go inside his house, then come out covered in blood. He tells detectives that Walter is dead and Fin arrests Jason for murder. Inside, they find Walter's bludgeoned body. Stabler immediately thinks Vivian did it and Benson is trying to protect her by accusing Jason.
Benson tries to track down Vivian, knowing Vivian is still mad at her for trying to keep Walter's identity a secret. She discovers Vivian has gone missing and goes back to the SVU, where Calvin is waiting. Calvin tells Benson that his mom dropped him off at the SVU and drove away. Benson looks at a letter that's in Calvin's hand and is shocked to fine that it's a notarized letter naming Benson as Calvin's legal guardian.