SPOILER ALERT: The following reveals major plot points from tonight’s NBC‘s One Chicago crossover.

NBC’s Chicago Med, Chicago Fire and Chicago P.D. came together for an epic crossover event taking the franchise to the next level.

Due to the pandemic, it has been six years since the One Chicago fam teamed up to take down some bad guys but they certainly made it worth the wait. All three shows are produced by Universal Television, a division of Universal Studio Group, in association with Wolf Entertainment.

In “In the Trenches,” Chicago’s first responders unite in the wake of a catastrophic gas explosion and fire that threaten a city government building. The episodes aired in a different order with Chicago Fire kicking off the night followed by Chicago Med and Chicago P.D. wrapping up the three-hour procedural extravaganza.

“This was an epic event, from start to finish. We started talking big ideas for the crossover very early in the season, and the story evolved over months and months,” shared Chicago Fire showrunner Andrea Newman via email to Deadline.

“The three amazing writers — Victor Teran (Fire), Stephen Hootstein (Med) and Joe Halpin (PD) had their own mini-room going for weeks as they fine-tuned the stories and character moves. We all really wanted it to feel like one big movie instead of three separate episodes. Then we had a rip-roaring Zoom table-read with all three shows, which was quite the thrill ride in and of itself,” she added.

Newman revealed via email the team took a 10-minute break during the Zoom and everyone showed off their pets.

Here is what she learned, “Steven Weber has a dog named Cat and Jessy Schram has a hairless cat named Pirate.” She did not reveal plans for Cat and Pirate to appear in a future episode but fans should start a campaign.

The experience of doing a major crossover was especially unique for Allen Macdonald, Chicago Med‘s newly minted showrunner who joined the series in its current Season 10.

“I basically got hired, started the Chicago Med writers room, and then Wolf Entertainment said: guess what?! We’re doing a crossover! It initially seemed like a daunting task for all involved, but I was impressed with how efficient the writing and production process was,” Macdonald said.

“And it’s just really helpful that the writers of all three shows are on the Universal lot in Los Angeles, and that all the cast and crew are on the same studio lot in Chicago… it made things so much more doable logistically. And I know all the cast members of the three shows had a blast working together on such a large scale,” he added.

At the center of tonight’s story, is an explosion that prompts the City of Chicago to unite its first responders to unite as one entity as chaos erupts. The injured are desperate to be helped as medical staff has to quickly assess and separate those who need life-saving care immediately from those whose injuries aren’t life-threatening.

The firefighters are focused on bringing down the flames and finding the source, a situation that Severide (Taylor Kinney) has been prepping for his whole life. P.D. faces their own challenges as they race against time to find the culprits and prevent further harm.

While all this is happening, Stella (Miranda Rae Mayo) is below ground in the subway at the same time as Ruzek (Patrick John Flueger), and they’re trying to hustle passengers out of the train and above ground to safety. However, their attempt was in vain. The structure above collapsed on everyone and now they’re all stuck back on the train with a limited amount of oxygen and patients in desperate need of medical attention. To add flame to the fire, pun not intended, they learn later that a suspect is possibly hiding among the victims in the train.

In a heroic act, Stella saves a teen using items she could find on the train while receiving instructions that were coming in choppy and were later cut early due to connection issues as they were underground.

Somewhere above ground, Archer (Steve Weber) is tending to a man who has become trapped under concrete and whose legs he will later amputate to save his life. Seeing Archer in his kind and humble moments with patients is the standout. When he joined Med, Archer was living in this grey area and was willing to do nearly anything to get ahead no matter who he hurt. It’s been nice to see him evolve across multiple seasons into who he is today. He is still a hothead and thinks he knows best about everything, but he seems to have been humbled by his hot-tempered exchanges with Lenox and by finding Goodwin (S. Epatha Merkerson) clinging to life after a stalker got very close to ending her life.

Seeing Archer, Voight (Jason Beghe), Pascal, and their respective teams working so close together, proves how much stronger they all are while working together across departments.

“It all starts with the characters. We take who and where the characters are and choose storylines that will challenge them the most and reveal new and surprising dynamics,” Newman commented on how they chose which characters for specific tasks and collaborations in the crossover.

She continued, “We also love to take characters that haven’t really interacted before, and that seem very different from each other (like Kidd and Ruzek), and throw them into a pressure-cooker situation together to see how they handle it, and what they bring out in each other.”

Gwen Sigan, showrunner of Chicago P.D. added about seeing team leaders working again together outside of a crossover, “I think it would be wonderful to have any of them back again — they each brought new and different energy to our set.  The pairings were great — we wanted them to be somewhat unexpected and to provide nice conflict with each other, so many of them ended up being foils. There’s certainly still a lot we could explore in the future.”

There are certain characters in the One Chicago universe that are sacred and who many would agree should be protected at all costs. Crossover writers threw that all out the window when they put Trudy (Amy Morton) and Mouch (Christian Stolte) through the wringer.

When we first see Mouch, he’s with his bestie Herrmann (David Eigenberg) lamenting a misunderstanding he had the night prior with his wife Trudy. After the explosion, Mouch and Trudy are reunited briefly and it’s clear the former is getting the cold shoulder from his spouse. Confused, Mouch does his best to stay out of her way, later learning there had been a misunderstanding between them. Trudy was somber and a bit peeved that Mouch had forgotten her birthday.

Trudy goes off leaving things up in the air with Mouch as she’s helping the team who is hot on the trail of persons or people responsible for the act of terrorism. Suspects were spotted briefly, but when they get away, Pascal sent Trudy to the garage to look for them.

A former P.D. colleague of Trudy’s, Bates (Jennifer Regan), is now working in security and is all over the case. She teams with Trudy in search of the bad guys but they split as each takes a different way down.

Bates bumps into Ruzek and Severide who were hot on the suspects’ trail before losing them. The scene pivots to Trudy as she exits the elevator in the parking garage where she bumps into a suspicious male character wearing a gas mask. She pats him down while pointing her gun at him as he pleads his case. He explained he was in the building to drop off some forms right before the explosion but Trudy isn’t convinced. She asks him to remove his mask but before he does so, someone shoots Trudy in the back three times.

In the end, it is revealed it was Bates who shot Trudy and that she was the insider who worked with the terrorists to enact their plan. It’s very touch and go for Trudy, who was taken to Gaffney Chicago Medical Center where she died a few times before her life was saved by Lenox (Sarah Ramos) and Ripley (Luke Mitchell) using an experimental surgery.

Mouch is relieved and grateful after his roller coaster of a day that almost left him a widower. We can be certain, Mouchy will never forget a birthday or anniversary ever again.

“It was probably a much more enjoyable storyline to write than to watch! We all knew that Christian and Amy would kill anything we gave them; they are such talented and reliable actors and also are pretty beloved across the three shows. It felt like the natural pair to hook our emotional throughline on,” commented Sigan.

Newman adds, “Ha! [Mouch] better not forget again. We’re obsessed with that couple. There’s so much emotion and love there — they found each other a little later in life, and they know how lucky they are. But Mouch has been so focused on work as he guns for the Lieutenant position that he’s let Trudy fall into second position.  That’s no place for Trudy Platt.  So it felt like the right time to heighten and challenge that relationship a bit, and bring some real, raw emotions to the surface.”

Speaking of Lenox, she was put in a tense situation by Burgess (Marina Squerciati) who desperately needed to question a patient she believed was one of the suspects. Lenox held her ground and could not break the rules as it could affect her patient’s health. Whether the patient committed a crime or not, doctors are bound by the principle of the Hippocratic Oath: Do no harm. Burgess’ frustration is so evident after an outburst, that Lenox finds a way to be flexible by sharing a nugget that helps solve the case.

“[Lenox] actually has immense pressure put on her to make a medical decision she doesn’t feel is in the best interest of her patient’s health. So she stands her ground and protects her patient, but still finds a way to help P.D. track down a new lead. Lenox is a rock star,” Macdonald said.

When asked about the future of Lenox and Archer’s relationship, he shared a cryptic note with Deadline.

“You’ll just have to watch to see just how much more bumpy things might become between her and Dr. Archer,” he said.

“How much more bumpy” implies so many things! I will truly lose it if Macdonald and the writing team set them up for a relationship beyond the professional. They are like water and vinegar! Stranger things have happened but I’m curious to hear all your theories.

Chicago Med, Chicago Fire and Chicago P.D. return with new episodes on February 5th. Newman and Macdonald shared whether or not their show’s storylines will pick up after the events of the crossover or if the special event was self-contained.

“In the past, we’ve done stand-alone crossovers, but this one is very much a part of the fabric of this season, for all the shows. What happens during the crossover will definitely impact these characters — and relationships — moving forward,” Newman said.

Shared Macdonald, “The crossover is definitely designed to exist as its own 3-hour experience, but it does not exist alone in the ether… it is organically and chronologically built into the current season of all 3 shows. So there will be post-crossover fallout for many OneChicago characters moving forward… some more than others. For example, Dr. Ripley and Randall “Mouch” McHolland have some tense moments in the crossover that will affect and influence their dynamic in an upcoming episode of Med.”