Entertainment TV 'SVU' : Mariska Hargitay's Olivia Benson Reconnects with Familiar Faces in Emotional 500th Episode Law & Order: Special Victims Unit aired its 500th episode Thursday night By Ally Mauch Published on October 21, 2021 10:00 PM Share Tweet Pin Email Mariska Hargitay on Thursday's 500th episode of SVU. Photo: Virginia Sherwood/NBC Law & Order: Special Victims Unit has marked 500 episodes 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 Mariska Hargitay, 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 (Danny Pino), 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." Virginia Sherwood/NBC Mariska Hargitay Says She Was 'Too Nervous' to Watch Law & Order: SVU's 500th Episode 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. This was confirmed when they headed back to his hotel room, though the intimate evening ended when they learned that the DNA evidence did indeed prove Ian's innocence. They successfully got him out of jail with the help of Olivia's old boss, Captain Cragen (Dann Florek) and defense attorney Trevor Langan — played by Hargitay's real-life husband Peter Hermann. Virginia Sherwood/NBC Isabel Gillies Reacts to Online Hate Aimed at SVU Character Kathy Stabler: 'Take It Down a Notch' Just outside of the courtroom, however, a shock was waiting for both Olivia and Burton: a woman accusing Burton of assaulting her years prior. Though the statute of limitations had passed on her case, a betrayed Olivia had her detectives look into Burton's past. What they found was a history of him using his prominent position to prey on (mostly younger) women — "an old school player," said Amanda Rollins (Kelli Giddish) — though nothing else criminal surfaced. Nick, meanwhile, began to see that Burton used him and his background in DNA to get close to Olivia again. "Nick, he wasn't trying to deceive you," Olivia insisted. "I asked him about that, he said that he wasn't sure how I would react. So I know that his wanting to free Ian Ridley is sincere." "Is it? Or is this about his career, his podcast? Liv, I'm angry right now," Nick argued, later adding, "I'm sorry I walked him back into your life." Virginia Sherwood/NBC "Please, I'm a big girl Nick," Olivia said, to which he responded, "Still, I mean, how old were you then? 16? He was 21? My daughter's 15." "It was a different time then. We were in love. Anything that we did I wanted to do, it was my choice," she said. "That's the thing about predators Liv, the good ones, the smart ones, they make their victims believe that," Nick, always protective of Olivia, continued. Olivia, however, decided to end the conversation there. "Nick, thank you, and I appreciate that you have graduate degrees, but I've also been here for a very long time so I don't need your expertise, but thank you so much," she said. "Physician, heal thyself," Nick quipped. Virginia Sherwood/NBC Christopher Meloni and Mariska Hargitay Troll Fans with Steamy Behind-the-Scenes Pic: 'Rehearsing What?' Once she got home, and poured herself a glass of wine, Olivia reflected more on her relationship with Burton and went back to his hotel room to confront him. "You slept with me when I was 16 Burton. You were 21. Technically, that is sexual assault," she said, after he had tried, and failed, to explain away the accusations that were brought up against him. "Oh, are you saying that you're a victim now? We were in love," he claimed. "I was a teenager, my house was a mess, you knew that — you knew that I would do anything to get away from my mother," an emotional Olivia said. "Please don't get her voice in your head," Burton said, referencing Serena. "We both know she was stone crazy." "Was she? Was she Burton? Or maybe, maybe she was trying to protect me," Olivia said before leaving and being thrust into another flashback from that dinner with her mother. Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories. "I hate him for what he did to you," Olivia said in the flashback, seemingly referencing Serena's rapist. "So do I," she said. "And if he hadn't, you would not be here." As she continued to walk away from Burton's, Olivia called Nick to issue an apology. "Nick, it's Liv," she said. "I wanted to tell you that you were right about Burton. And I'm sorry for being so defensive. And thank you." Law & Order: Special Victims Unit airs Thursdays (8 p.m. ET) on NBC.