In the special two-hour season premiere of Law & Order: SVU, the team suspects serial killer Greg Yates (Dallas Roberts) has struck again after a redheaded woman's dismembered body washes up by his former burial ground. Detective Amanda Rollins (Kelli Giddish) visits Yates in jail to find out if he had a connection to the murder. He claims to be innocent, but ominously suggests that he might have some better info if Rollins returns in a few days. Back at the precinct, the victim is identified as Brooke Groves. However, when Detective Olivia Benson (Mariska Hargitay) and Detective Sonny Carisi (Peter Scanavino) go to her house to inform her family of her death, they find Brooke alive, but learn the victim had a troubled twin sister, Rachel. Brooke goes to the morgue and confirms that the body is Rachel's.
At the homeless shelter Rachel frequented, a worker tells the detectives Rachel left a few months earlier with an old woman, whom the detectives can't identify off security footage. Rollins returns to Yates, who suggests looking into the house of one of his former medical school friends. Once there, SVU finds a mummified corpse chopped up and hidden inside a chimney. When Rollins returns to ask Yates for more information, he requests a conjugal visit from his fiance, Susie Frain, in return. After the visit, both Yates and Suzy say that the mummified body belonged to Lena Grunwald, who was murdered by Grunwald's former fiance, Carl Rudnick (Jefferson Mays)... who happens to be the Deputy Chief Medical Examiner, the man who had just claimed that the mummified corpse was unidentifiable.
Although the team is ready to ignore the accusations against Rudnick, Carisi convinces them to look into it. Benson and Fin visit Susie Frain again, who says Grunwald was a Swiss national who had a rocky relationship with Rudnick. Grunwald once told her that if anything bad happened to her it would be Rudnick who did it. When Lena disappeared 13 years ago, Susie almost called the cops, but decided not to when she received a photo of Grunwald back in her Swiss village.
After the team confirms Rudnick lived in the house where Grunwald was murdered, Benson asks M.E. Warner to re-autopsy the two bodies. Warner reveals Rudnick's autopsies were not accurate, and it was clear the mummified body was Lena. Meanwhile, Carisi looks into the theory that Grunwald returned to Switzerland and learns there are records of her flying there, but not returning. There are also records of Rudnick coming home from Europe, but never flying there. He speculates that it's possible Rudnick used Grunwald's passport to fly there, pretending to be her. Carisi's theory is corroborated when the team finds women's dresses and wigs in Rudnick's closet.
Rudnick is arrested, but immediately posts the $2 million bail. Meanwhile, facial recognition confirms that it was not Lena who flew to Switzerland, and the photo Susie received from her friend was actually of Rudnick in drag. Unfortunately, Susie's apartment was ransacked and the photo stolen, and not long after, her body is found chopped up on a beach. When Rollins tells Yates, he asks for the ME to check if Susie was pregnant. He also believes Rollins is pregnant based on her scent. She takes a pregnancy test; it comes back positive. In the midst of all of this, Rudnick goes missing. The team locates him in Buffalo under one of his aliases, presumably trying to cross the border. It turns out Rudnick murdered the people whose identities he was using.
When Rudnick goes to trial, the defense makes a strong case and begins to win over the jury. In a last-ditch effort, the SVU decides to follow the new lead that Rudnick constantly talks to himself. They review the footage of their interrogations and find that Rudnick had actually confessed to himself when he was alone in the cell. When this evidence surfaces, Rudnick pleads guilty to the murder. Rollins relays this news to Yates, and he comments on how they are starting to form a relationship. Rollins leaves, uneasy at how close she has grown to the serial killer.