has marked with an emotional five-act installment that dove deep into Detective Olivia Benson's past and, of course, featured the crime drama's characteristic twists and turns.

Olivia, played by , had a flashback at the start of Thursday's episode to a dinner she had with her late mom, Serena, during season 9. During the dinner, Serena asks Olivia to leave behind her job with the Special Victims Unit.

Olivia has a complicated history with Serena, who became an alcoholic after she was raped and got pregnant with Olivia. The flashback marked the first of many familiar faces fans, and Olivia, saw throughout the episode.

When she arrived at the station after dropping son Noah off at school, she was surprised to find her old partner, Nick Amaro (), waiting for her in the interrogation room. Nick served at SVU for several seasons before the actor's departure in 2015.

"You're a captain now, you don't like surprises?" he teased Olivia, who joked, "I've never liked surprises."

Nick revealed that he had pivoted to studying DNA and genetics, and that he was at SVU regarding a closed case in which a teenager was killed on her prom night several decades earlier. Her date, Ian, confessed to the murder in a panic at the time, he said, but didn't actually do it, and Nick sought to exonerate him by pulling out old DNA evidence.

Nick's partner in exposing the case turned out to be an old friend of Olivia's, an author and podcaster named Burton (Aidan Quinn). Via another flashback, viewers learned that Burton was actually a former boyfriend of Olivia's, a college student she dated when she was a teenager. They got engaged but broke up when Olivia's mom forbade the relationship.

As they worked on solving the case, it was clear that the romantic tension remained between Olivia and Burton.

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