Credit: Virginia Sherwood/NBC

The Law & Order: SVU cast might not be part of the Marvel Cinematic Universe, but they’re about to enter an “Endgame” of their own.

Thursday night’s season 20 finale of the NBC crime procedural shares that title with the recent Marvel blockbuster, and while aliens and superpowers may not be running rampant, guest star Titus Welliver (Lost, Bosch) tells EW that a “major, major showdown” is looming between his character, Rob Miller, and Lt. Olivia Benson (Mariska Hargitay).

Welliver’s character has been accused of rape, but despite the SVU squad’s best efforts, they haven’t been able to keep him behind bars. Previews for this episode have called him “the most powerful criminal Benson’s ever faced” — which is pretty big thing to say when you’re talking about a show that’s been facing down bad guys for two decades. But Miller isn’t your average perp. “He’s a political animal, so it moves to a different place,” Welliver explains. “He has that political influence — he’s a fixer, kind of a Roy Cohn character.”

And now that he’s out of jail, he’s placed Benson firmly in his crosshairs, trying to intimidate her into dropping the case against him. In an unsettling moment last week, he dropped by a restaurant where Benson and Noah (Ryan Buggle) were sitting and introduced himself to her son. When Miller touched Benson’s shoulder during the encounter, that invasion of her personal space “definitely fired up the viewers,” Welliver notes.

“[Benson’s] not afraid of anyone, but she doesn’t know what he’s capable of — I mean, she has an idea, and it’s pretty serious,” he says.

In Thursday’s finale, a teenager is found dead in the Hudson River and Benson suspects Miller has something to do with it, but she can’t prove it. Despite only having circumstantial evidence, ADA Stone (Philip Winchester) takes the case to court in hopes they can stop Miller before he destroys more lives.

And then there’s the question of what that “Endgame” title means, and who (or what) it’s an endgame for. “Everything that has transpired up into this episode culminates into a major, major showdown,” Welliver teases. “People always say, oh you know, it’s the season finale, she’s going to get the bad guy and then we’ll all be done. But there’s a big question mark about that. Is it going to be done? Will there be genuine closure? There are a lot of different variables that could contribute to this ‘endgame.’”

And, since the show has already been renewed for a historic 21st season, it’s probably safe to assume there’ll be some fallout from whatever that conclusion is. As Welliver cryptically puts it, “Nothing’s neat and with a bow.”

The season 20 finale of Law & Order: Special Victims Unit airs Thursday at 10 p.m. ET on NBC.

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