'Chicago Fire' Boss on Kidd and Severide's Tense Reunion: You 'Should Be' Very Worried (Exclusive)

Chicago Fire
Adrian S. Burrows/NBC

Showrunner Derek Haas breaks down the final moments in Wednesday's fall finale.

Spoiler alert! Do not proceed if you have not watched Wednesday's fall finale of Chicago Fire.

She's back! After an extended hiatus, Chicago Fire star Miranda Rae Mayo returned at the end of Wednesday's fall finale, the unexpected timing of her character, Stella Kidd's, re-emergence complicating matters for Severide (Taylor Kinney). Though the episode directly addressed Kidd's prolonged absence on the show (due to her commitment to her Girls on Fire program), her return opens a new can of worms -- and problems -- for the couple.

"The timing of her leaving wasn't ideal professionally with the open spot for the lieutenantship or with Severide, because Severide had a history of going a little off the reservation on her in the past. But she's never really done that to him," executive producer and showrunner Derek Haas tells ET of the episode's tense reunion. "And so he doesn't know quite how to react to that situation of being ignored... or abandoned for the most part, even if the reasons were good and noble. This is going to be a source of concern going into the second half of the season."

This only means the couple, currently engaged, is going to be facing a rocky road when Fire returns in the new year.

"Unfortunately with Severide, communication is not his strong suit, so that's going to come back into play. True to his character is maybe not the best communication happening between him and Stella when she returns," Haas previews. "There's a lot to talk about -- it's both her place at the firehouse and her place with her relationship with him that's going to need some major work-in-progress-type renovations." He emphasized the last part of his answer once more: "Major renovations."

The show's winter return will pick up "immediately after the events of [episode] No. 9," Haas teases. "No. 10 starts right in the aftermath of that. You've got a situation where it's musical chairs [at Firehouse 51] and there's one too many people and not enough chairs, so that's going to come into play."

Haas also spoke about welcoming Mayo back into the Fire fray.

"It was awesome. She was very much missed. We love her. Watching episode 10, I was just beaming -- I love Miranda anyway -- but getting to see Stella Kidd in action is always fun for me," Haas praises. "So I was smiling ear to ear watching her back onscreen. No. 9 doesn't leave you with a lot of warm, fuzzy [feelings], so it was nice to see her back in the scenes."

Asked whether fans should be worried about the future of Kidd and Severide's relationship, Haas offered this warning: "Yeah, you should be for sure."

Chicago Fire returns Wednesday, Jan. 5 on NBC. For more, watch below.

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