Chicago Fire’s Eamonn Walker Teases His Return to Firehouse 51 (Exclusive)

Here’s the good news: Eamonn Walker is returning to Chicago Fire as Wallace Boden in this week’s episode. But here’s the bad news: Boden’s return is bad news for Firehouse 51.

“Unfortunately, a terrible situation,” Walker, 62, tells PEOPLE of his first episode of the hit NBC drama since his departure last May. “There’s a fire that 51 thought was over and done with until they heard an alarm go off and then realized that they left a man behind. That person has ended up in the hospital and we may potentially lose them.”

The cause for concern doesn’t end there.

“Because of that, almost straight away, an investigation starts and Deputy Commissioner Boden turns up at 51 to find out what happened, whose fault it is, and then maybe a head will roll,” Walker adds. “So not only do you potentially lose one of your 51ers in hospital, you potentially lose one because I fire them.”

Read on for more of Walker’s warnings about the April 16 episode and details of his bittersweet return to the set.

PEOPLE: How did it feel for you to be back on set? 

EAMONN WALKER: The welcoming was so warm. I had missed them terribly and to find out that they had missed me as much was fantastic. There were tears for arriving and starting filming the first day, and there were tears at the end when I left. One is always happy if one knows that one’s left one’s mark somewhere, and what I didn’t realize until I left was how much everybody had left their mark on me. So it was a real pleasure to be back. 

When you return to certain places, especially where you’ve spent a lot of time, it can be a bit of a sensory overload. Was there a moment when you first set foot back on set that hit you like that?

There were many. The weirdest moment was very quickly after I go and talk to all the officers and the chief. This wasn’t a moment in the script, but I ad-libbed it anyway because I had to acknowledge it within myself because I was feeling it. I turned round to Dom [Pascal, played by Dermot Mulroney] and I go, “Your office, let’s go.” And he goes, “Oh, okay.” There are all of those feelings because I’m standing in an environment that I stood in all of this time, but I had to acknowledge that I’ve actually got another office in another building, and I had to let all of this go. And that happened in the scene while we were filming it. I didn’t even know I was going to say it. So you’re right. There’s things that come up. 

So do you think maybe for the next season, you would do more than one episode? 

If they write it. It’s all about the storyline. You need to talk to Andrea [Newman, an executive producer] about that. Because when they wrote this episode and said, “Would you come and do it?” And I read it and was like, “Yes, sign me up. Where am I going?” It’s an amazing episode, a wonderful piece of writing and shot in a way that has not been shot before as far as I was concerned, written in a way that has not been written in all of the years I was there, I never saw an episode written like this.

Have you continued to watch the show regularly? 

I haven’t watched the show because it’s painful. OK? I don’t want to go down memory lane every single time I watch it. But I think that’s been a really good thing. I was able to go in fresh and and not be carrying any kind of baggage about what I’d seen or what had been happening. The last time Boden was there was the last time I was there. And so I walk in with this heightened scenario, and none of that other stuff, none of those other relationships, none of those politics matter. What’s on the line right now is somebody may live or die in a couple of hours, and I need to know why and whose fault. And if I deem it’s your fault, I’m sorry, no matter how much I love you, you’ve gotta go.

You’re making me so nervous! Did you have any conversations with Dermot Mulroney about stepping into that leadership role?

We had lots of conversations about it. He’s such a lovely man. We really enjoyed each other. So it was fantastic to do scenes with him. But the heightened situation took away from everything. Because I was in every scene with every officer, so I was on all the time, so there was very little time for just chatting. But yeah, we enjoyed each other. 

What do you think about how Mouch (Christian Stolte) and Hermann (David Eigenberg) are doing with following the path to advancement that Boden tried to set for them?

I think it’s wonderful when you give somebody advice and in some shape or form — and to a less or greater degree — they’re actually doing it, I think that’s great. It also makes those two characters, in particular, take on board the job that Boden was doing while he was there. There were times he made it look easy, but it’s not an easy one. You take responsibility of everybody’s life in your hands and so it explains a lot about why he didn’t smile. Boden didn’t smile a lot because when you have the weight of somebody’s life in your hand, it’s heavy. It’s a heavy load. And it takes some getting used to — and I think those two will get used to it eventually.

What are you working on now? What’s next for you? 

I’m not working right now. I’m just doing family right now.

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Chicago Fire airs Wednesdays at 9 p.m. ET/PT on NBC.