• ‘Law & Order: SVU’ Season 18 Spoilers: VP Joe Biden to feature on Sept. 21 episode.

‘Law & Order: SVU’ Season 18 Spoilers: VP Joe Biden to feature on Sept. 21 episode. (Photo : Facebook/ Law & Order: Special Victims Unit (SVU)/ NBC)

"Chicago PD" and "Law & Order: SVU" will have a four-part crossover episode this season.

In an interview with The Hollywood Reporter, "Law & Order: SWU" showrunner Warren Leight dished on what fans can expect from the tumultuous episodes.

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"I was trying to wrap my head around a story that would touch all of those bases. I was trying to think what case starts to in a hospital, goes to a fire station, goes to New York and then goes back to Chicago," he said.

Meanwhile, Leight said that he initially proposed that the crossover should air on a Wednesday night, but this wasn't approved.

"That didn't go over too well because they wanted it to be on two consecutive nights. Out of desperation I said, 'Dick, what if instead of the four-way, we did a perfect 'SUV-to-'P.D' hand off.' And Dick said okay, which is Dick excited," he said.

In other news, Leight revealed that the crossover will focus mainly on the toughest characters to have ever been on the show. More specifically, the crossover will see the return of series killer Greg Yates (Dallas Roberts).

Last April, Greg killed a recurring character on "P.D" named Nadia. Greg was last seen serving a life sentence in an upstate New York City prison.

"We had one little scene with Rudnick and Yates sitting down in the cafeteria that I threw in at the last minute while we were shooting the episode because I thought, 'Well, wouldn't these two be great prison bunkmates?' and then the David Sweat prison break happened last spring," he explained.

When asked what exactly will happen to Roberts' character, Leight said that the only logical thing was for the serial killer to be able to escape prison.

Meanwhile, the crossover will kick off with Greg asking Rollins (Kelli Giddish) to visit him in prison. He will lure Rollins by saying that he has some valuable information about women.

However, despite her desire to not have anything to do with Greg, Rollins will find herself being lured by this character yet again.

"Law & Order: SVU" airs Wednesdays at 9 p.m. ET and "Chicago P.D" airs at 10 p.m. ET on NBC.