Calvin is growing more and more attached to Benson, even going so far as to draw a picture for her and signing it "Calvin Benson". The detectives are assigned to investigate the death of a young woman named Caitlin, who received massive head trauma at a party. Caitlin was taken to the hospital and later died. Warner discovers that the victim had sex, but she can't tell whether it was consensual or not.
Caitlin kept a list of all the men she'd slept with, and one of her partner's is the boyfriend of the woman who threw the party. Jill admits that she invited Caitlin to her party in order to get revenge, and she attacked Caitlin, shoving her against a mirror.
Warner notices blue gel inside Caitlin, which turns out to be residue from a defibrillator machine. Warner thinks that the paramedics might have attacked Caitlin the ambulance. The detectives speak with the two drivers, eventually figuring out that one of the men would rob the patients and the other would rape them.
Stabler believes that the two men would give each other up if questioned separately, and one of the paramedics, Mike, caves in, confessing that he would steal from patients before his partner, Tinta raped them. Mike is wired up and sent to speak with Tinta, hoping to get him to admit to the crime. Tinta suspects something is up and runs towards the ambulance. He injects something into his jugular and loses consciousness.
Stabler tells Benson that there's evidence that Vivian may be linked to the robberies, but Benson initially doesn't want to track Vivian down, claiming that they might run into a dead end. Stabler accuses Benson of not wanting to follow up on Vivian because she's reluctant to give up Calvin. Stabler also says that he knows Benson didn't send the DNA sample to the lab, to find out the identity of Calvin's father.
Cragen takes Benson off the case since Vivian's involvement and Benson's guardianship of Calvin could mean a conflict of interest. Benson tracks Vivian on her own, and she finds her, once again high. Vivian asks Benson to leave her alone. If Benson leaves, Vivian promises to give Calvin completely over to Benson. Instead, Benson arrests Vivian.
Vivian confesses to killing Burlock, the rapist who attacked her mother and fathered her. Cragen chews out Benson and Stabler for disobeying him and finding Vivian. Suddenly, Vivian's friend Sarah comes into the station and claims that she killed Burlock.
Vivian says she was trying to protect Sarah by claiming she killed Burlock. Sarah is arrested and charged with murder, while Vivian is expected to be sent to rehab via court order. Benson realizes that once Vivian makes bail for herself and Sarah, she'd just go back to the drugs.
After Sarah and Vivian are released on bail, Vivian speaks with Benson, demanding that she be allowed to see Calvin. However, Benson thinks that seeing his mother may traumatize the boy. Gunshots are heard. Benson orders Vivian to stay put and then goes to investigate. Sarah has been shot dead, and Vivian blames Benson.
Warner finds DNA evidence on Sarah's body which is a match to Calvin, meaning that the murderer was Calvin's father. The DNA belongs to Vivian's ex-boyfriend, David. He confesses to the crime, saying he killed Sarah for taking Vivian and his son away from him.
Later at SVU, Stabler is with Benson and Calvin when Child Protective Services arrives to deliver papers to Benson, terminating her guardianship of Calvin. Vivian shows up and hugs Calvin. The CPS agent explains that Calvin will be put in the custody of his father's family as Vivian goes into rehab. Calvin clearly doesn't want to leave Benson's side, but Vivian grabs him and drags him away.