One Chicago Crossover Will Be ‘Massive,’ Include ‘Really Neat’ Pairings and Feel Like a 3-Hour Movie (Exclusive)

After a six-year drought, One Chicago fans will get a three-show crossover of epic proportions — and Us Weekly has learned all about the TV event.

“The keyword here is massive,” Chicago Med star Steven Weber, who plays Dr. Dean Archer, exclusively told Us of what’s to come on Wednesday, January 29. “The situation is massive. The amount of actors in all the shows is massive.”

He teased that Chicago Med, Chicago Fire and Chicago P.D. coming together and interacting is “ridiculous” and unlike anything they’ve done in the past.

“It’s not just a few here and maybe two here,” Weber, 63, shared. “I mean, it’s, here comes everybody and it’s gonna be a huge event.”

The episode, titled “In the Trenches,” will begin with Chicago Fire, which is a change from the regular One Chicago Wednesday lineup that usually begins with Chicago Med. Fire will be followed by Med and then P.D. will wrap up the night.

“When a gas explosion rocks a high-rise, Chicago’s first responders come out in force to rescue hundreds of civilians,” the official logline reads. “It’s the calamity beneath the surface, however, that sends our heroes on a race to save 40 people trapped deep underground, including two of their own.”

While the names of the two first responders trapped haven’t been confirmed, Weber told Us that the showrunners “put all their creativity and their might into making this crossover,” teasing, “It was the most fun I ever had.”

Joe Miñoso, who plays firefighter Joe Cruz on Chicago Fire, is equally as excited to see what fans think of the mega event.

“This is not a crossover night. This is a three-hour film. This is a movie that happens to have all of your favorite One Chicago characters in it,” he dished to Us. “It is so large in scale, it is bigger than anything we’ve ever done. It is insanely impressive.”

Miñoso confessed that he’s not sure how production “managed to pull off” the three shows meshing so seamlessly.

“It was an incredible feat and I’m so proud to… just even remotely knowing these people because it was really amazing what we put together,” he added.

Chicago P.D. showrunner Gwen Sigan exclusively told Us that her show’s characters will keep the story line moving as the Intelligence Unit tries to solve who is to blame for the explosion.

“We’re a lot of the engine of the investigation, obviously, and making sure that we get these offenders that were part of this criminal incident that happens in the first episode,” Sigan explained.

She promised “some really neat pairings,” noting, “Between our show and Med and Fire where we usually don’t get our characters together for this long. And so that’s fun.”

Sigan added: “We’ll definitely have characters sort of in some tough situations and then also characters sort of racing against a tick clock to hopefully get everybody outta those situations.”

Looking ahead, Sigan said viewers should prepare for a “fun ride,” telling Us, “I’m proud of it. I think that all the shows really came together as best as we could to make something really engaging and exciting.”

“It’s really good,” she added.

The One Chicago crossover event airs on NBC Wednesday, January 29, starting with Chicago Fire at 8 p.m. ET. Chicago Med airs at 9 p.m. ET with Chicago P.D. following at 10 p.m. ET.