The body of a seven-year-old child reported missing in 1980 is found and the squad begins to investigate convicted serial killer Lucas Biggs (John Savage) who is on death row in Virginia. While Biggs can detail every child he ever molested, he swears he has no memory of this one. The squad learns that the boy was killed by one of Biggs' former victims (Terry Serpico) who, unbeknownst to his wife (Angelica Torn), lives a secret life as a child molester passing on the abusive habits he learned. Someone kills the suspect before he can be picked up. When a man (Michael Shannon) confesses to picking off a rapist, the detectives need to decide whether he committed the crime or whether he confessed out of trauma and shame.
Complications ensue in the investigation of a gangbanger who fell off a building after the victim that he tried to rape bit him in self-defense. When Detectives Benson and Stabler are sure that they have found the victim (Reiley McClendon), his twin sister (Reiley McClendon) admits to biting the gangbanger even though the bite came from someone who was chromosomally male. The twins are shocked at the revelation that their parents (John Bolger and Hillary Bailey Smith) tried to raise one of them as a girl after a botched circumcision. Investigation reveals more regarding the ulterior motive of a doctor (Peter Firth) to prove that nurture supersedes nature.