'Chicago Fire' Recap: 'Law & Order: SVU,' Chicago P.D.' Stars Crossover

Dick Wolf, the famed "Law & Order" producer has long used crossover episodes to boost his shows.

That was always easy in the "Law & Order" universe because the show shared the same city, minor characters, and timeline.

The same has been true in the world's of "Chicago Fire" and "Chicago P.D.," shows that take place in the same neighborhood sharing sets and storylines.

Tonight, however, Wolf takes things a step further by kicking off a massive three-part crossover episode on "Chicago Fire" which continues later this week on "Chicago PD" and "Law & Order: SVU."

The case the three casts will all become involved in began on "Chicago Fire" when the team fights a house fire and Kelly Severide (Taylor Kinney) sees a man run into the burning building to get a mysterious box.

The box appears to contain child pornography, and '"Chicago P.D.'s" Hank Voight (Jason Beghe) and Erin Lindsay (Sophia Bush) are called in to help investigate.

"The original case was much less disturbing and I said, 'On no planet would New York SVU fly to Chicago for what could be possibly statutory rape or endangering the welfare of a child," Leight told TVGuide.com.

"If you're going to cross these shows over, it has to be an exceptionally disturbing crime.

In reality, there are kids being sex-trafficked in America, being forced to perform in videos, and those videos are streamed live and they're basically being assaulted for the enjoyment of people watching on computers."

Of course, the producers need a way to bring the "SVU" cast in, so the pictures are discovered to have been taken in New York, so Lindsay calls to "SVU'"s Det. Amanda Rollins (Kelli Giddish).

Lindsay, Voight and Jay Halstead (Jesse Lee Soffer) then fly to New York on Wednesday's episode of "SVU" before the crossover finishes on P.D. Wednesday at 10.

This is "Fire's" third season, "P.D.'s" second and "Law & Order: SVU's 16th." Mariska Hargitay has been playing Olivia Benson since the show's start in 1999.

"I love her more now than ever...I love her because I am challenged by her," Hargitay told reporters on set of Law & Order: SVU. "I never know what's going to happen. She surprises me.

[Warren Leight] surprises me. This character has evolved, which is the most exciting part of it. I feel in many ways she's a new character because she's gone through so much that has truly transformed her."