This is not a drill, Chicago Fire fans: Eamonn Walker is guest-starring as the beloved Chief Wallace Boden in tonight’s (April 16) episode! It’s set to be a thrilling reunion among the firefighters. 

Chi-Hards have patiently awaited Boden’s return since Walker’s Season 12 exit from the show’s regular cast. Boden may no longer be at the helm of Firehouse 51, but he’s not far from his former home as the Deputy Commissioner of the CFD. But as Boden finally reunites with his Firehouse 51 family, the circumstances are less than ideal; a tragedy will summon his presence and put him at professional odds with his friends in the upcoming episode (Season 13, Episode 18: “Post Mortem”). A description teases, “Deputy Commissioner Boden returns to Firehouse 51 to investigate a disastrous firefight and the surrounding mystery that left one of their own in peril.”

Which firefighter’s life is on the line? What will Boden make of the madness? NBC Insider chatted with Walker ahead of the episode, and let’s just say Boden’s not playing favorites as he returns to Firehouse 51. This Deputy Commissioner means business.

Read our conversation with Walker, below: 

NBC Insider: Welcome back! Everyone is so excited to see Boden again. What was it like to return to Firehouse 51?

Eamonn Walker: It was amazing. I had a wonderful time. I had missed everybody. They had missed me. And so the coming together was very emotional. But because we were on that tight schedule, we had to kind of get past all the emotions and get on with it. And the crew, the cast, the people in the office, it was just great to kind of be back and in the slipstream of it all. So I loved it.

RELATED: What Happened to Eamonn Walker’s Chief Wallace Boden on Chicago Fire?

NBC Insider: What have you missed the most since leaving Chicago Fire?

Eamonn Walker: The people I know and love. You know, it’s my family. It’s my extended family. And so getting them back in my life and being able to laugh and joke and work and connect was everything that my inner being had been missing in the time I’d been away. And it was like a jolt to my spirit. I was very, very happy to be back, and I would have to say that the welcoming was amazing, too. They welcomed me home.

NBC Insider: What can you tease about the upcoming episode? 

Eamonn Walker: Well, can I tell you? What can I tell you? [LAUGHTER] Here’s what I will tell you. You can expect something that you’ve never seen before. This whole episode is not a normal episode of Chicago Fire. Even from the way it’s filmed, the structure of the piece, and what’s happening to your dearly loved members of Chicago Fire.

One of [the firefighters], during the episode, his life is on the line. And so because of that, because something went wrong in a fire, it’s somebody’s fault. And that’s the reason why Deputy Commissioner Boden has to come in immediately. We don’t even know during the episode if this person is gonna live or not. But the investigation needs to happen right now. So we know what’s going the way forward. And so that’s very unusual for Chicago Fire.  

NBC Insider: It seems like Boden will inevitably cross paths with Chief Dom Pascal in the upcoming episode. What was filming those scenes like?

Eamonn Walker: To work with Dermot [Mulroney] was amazing. And he fits in with the Chicago Fire scene — the joking, the working, the difficult situations, weather, and all the rest of it. He fits in like a glove, so that was great. It was good for me to be working with him.

But all people who are in charge of anything that happens at Firehouse 51 —so all lieutenants and the chief — are on the line for this person who potentially is ‘gonna die by the end of the episode. So, heads may roll. And so if a head’s ‘gonna roll, I have to put everybody through their paces, including Dermot. It’s a potential firing that’s on the [line], especially if this person dies. And so it’s very, very serious, and everybody’s on their toes.

NBC Insider: It sounds like the happy vibes behind the scenes were in stark contrast to Boden’s in-episode reunion?

Eamonn Walker: Yes. [LAUGHTER] Well, that is always the case with Chicago Fire. You know, what happens is we’ve got people who, as in the real fire department, you walk into a situation where somebody is desperate — they’re hurt, or their house has been burned, or they’re stuck in a car, or they’re losing their life. And first responders, they’re the first person to you in that terrible moment. And so not only do they lose people, they also lose each other.

And there is a gallows humor to keep themselves going. It’s a necessary thing for the mentality so you can move forward. And we have a version of that within the show. We have these really tough, strict, deep scenes. And then, the moment they shout cut — it’s a good job there’s no camera, that’s all I’ve got to say. And when there is a camera, we shoo them away because we’re terrible. [LAUGHTER] If you knew exactly how much laughter there was, you would turn around and say these guys are not working. This is not work.

RELATED: Why Did Chief Wallace Boden Leave Firehouse 51 on Chicago Fire?

NBC Insider: What’s your favorite part about being a part of this One Chicago family where it’s not really goodbye, just see you later?

Eamonn Walker: Once a part of the Chicago Fire family, you’re always a part of the Chicago Fire family. And so it doesn’t matter where you are or what you’re doing. If you knew exactly how often I speak to this cast and the crew — I’m always on the phone with them. And in some ways, it feels like I’ve always been there ’cause I’m always on the phone with them. That’s to let you know the family aspect of it. It’s not just some slogan… It started with us. We were real. We were keeping each other — in a very cold climate during a polar vortex — we were keeping each other going, and it’s never stopped since. 

Don’t miss Boden’s return to Firehouse 51 by watching Chicago Fire Wednesday, April 16 at 9/8c on NBC and next day on Peacock.