Benson was disappointed to hear that Cragen was being temporarily re-assigned because of her and Stabler's screw-ups from the past. To make things even more awkward, Munch was taking the role of Sergeant, while Cragen is moved. Munch defended his role, saying he took the Sergeant's test a year ago and had no idea he would pass.
Benson and Stabler were investigating a missing woman and her young daughter. They believed the woman was assuming alternate personalities and putting her toddler at risk. The detectives tracked down Dr. Carlisle, her psychiatrist, in hopes he could shed light on their case.
Stabler and Benson interviewed April's old babysitter about Janis's mental behavior. Penny, the babysitter, said she was fired, but Janis was the one who was unstable. She was always late picking up her daughter and hysterical when Penny would confront her on it. But, another babysitter said that Janis was completely stable and said Janis could be found at her job at the Metropolitan Museum of Art.
Benson and Stabler tracked down Janis in a Manhattan park, where she was crouched down with an empty baby carrier. She had no recollection of a baby. She began to assume the identity of a small girl by the name of Tammy. They took her in for questioning.
Benson went back to check on "Tammy" and her lawyer, but found a new personality. "Dory" was in the middle of firing her lawyer. The lawyer stated he had to be fired by his client and not her alternate personality. Stabler told "Dory" to sign the waiver papers as Janis and then the lawyer would have no more rights as her attorney. "Dory" then took an unhealthy liking to Stabler.
Dr. Carlisle came in to try to get through to Janis by using hypnosis. Janis stated that she remembered seeing April that morning when she gave her a bath and then saw April in the cave, where Janis was working. Stabler let Benson know he was sure Janis killed her baby.
After Sergeant Munch used the media to try to find April, a young woman came forward claiming to be April's real mother. When interviewed, Cass said Janis was her older sister and she moved to New York shortly after April was born. Janis cared for April while Cass served time in prison. Meanwhile, one of Janis's personalities, Dr. Yang, was denying that Janis even had a sister.
Stabler and Lake continued to interview Cass. They found out that Janis left home when she was just 16 and when she left; Cass was severely abused by their father. Janis was forced to watch as her younger sister confessed that their father started to rape her when Janis ran away from home. "Dr. Yang" couldn't believe Janis would leave her younger sister like that. Meanwhile, Cass's story panned out, April was safe and sound at her apartment.
Janis re-emerged and was confused on why she was in the police station and why her sister was also there. Benson didn't want to release Janis into her sister's custody, but Dr. Carlisle insisted that neither Janis nor her personalities were dangerous.
Benson and Stabler joined Warner at house of Janis and Cass's parents, where they were each shot to death. Stabler and Benson were sure that Janis was the one who killed them. Stabler was interrupted when Kathy called him with an emergency; Janis was at his house with a knife.
Stabler and Benson rushed to his house to find cops surrounding the premise. When Stabler appeared inside, he saw "Dory" talking to Kathy while holding a knife. Stabler interrupted their conversation and "Dory" told Stabler she got his address when she was snooping around at the precinct.
Once Kathy was able to escape, Stabler and Benson teamed up on "Dory". She told them that "Bert" was going to come after her and that he was responsible for killing her parents. She was put into a psychiatric ward and Novak was busy trying to prepare a case. Dr. Carlisle apologized for not working on "Bert" as a dangerous personality.
Novak still put Janis on trial. She wanted to know what made Janis all of a sudden snap and murder her parents and questioned Dr. Carlisle about it. Novak then questioned Janis about the murder of her parents. Janis had no recollection of that night, even when Novak presented her with evidence, the shotgun used on her parents. Just then, another violent personality emerged and tried to strangle Novak and she was carried away.
Janis was found not guilty by reason of insanity. When Novak took a closer look at a picture of Cass, she noticed a law book in the background. Novak was convinced that Cass had studied law while in prison in hopes of helping her sister murder her parents. Stabler and Benson decided to pay Cass's cellmate a visit in prison.
Cass's cellmate confessed that Cass and Janis were plotting the murder of their parents. Stabler and Benson decided pay the sisters a visit. Janis told the detectives there was nothing they could do to her because of double jeopardy. Stabler then decided to put Cass under arrest for her participation in the murder. Janis started to flip out, but there was nothing she could do about it. Stabler told Cass she might have well pulled the trigger, herself.