the hit NBC drama for the first time since February 2023 Chicago Fire season 12

is really heating up! And that is meant quite literally, as the new season of the NBC

hit kicked off with Stella Kidd (Miranda Rae Mayo) and her husband, Kelly Severide

(Taylor Kinney), taking a steamy, steamy shower. The scene marked Kinney’s first on the show since Feb. 22, 2023. In January of last year, the actor, 42, took a leave of absence from the show “to deal with a personal matter,” a source close to the production told PEOPLE at the time. Kinney’s was the first of several happy returns in the new episode, which picked up six months after last May’s season finale. At the end of season 11, Matt Casey (Jesse Spencer), who now lives in Portland, Oregon, proposed to his ex-girlfriend Sylvie Brett (Kara Killmer); Randall “Mouch” McHolland (Christian Stolte) flatlined after being struck by a bullet during a call; and Stella was heading south to find Kelly after he never returned home following his arson investigation training course.

In the premiere, Kelly was back at Firehouse 51, Mouch returned to work for the first time after recovering from his ordeal, and Sylvie was rocking Matt’s rock. But all was not completely hunky-dory at the station. Despite their pre-shift shower, Stella and Kelly were on shaky ground. Stella’s trust has been broken, so she was hesitant to allow Kelly to get involved in any arson investigations lest he leave her — and 51 — behind again. Of course, she had to let that go somewhat when there was an arsonist on the loose targeting firefighters. While Sylvie was excited to marry Matt, the wedding, she said, is in about a month and a half — and she’ll be leaving Chicago afterward. (Killmer’s departure from the show sometime this season was confirmed in November.)

Blake Gallo (Alberto Rosende), however, had already left the firehouse as he prepared to move to Michigan to be with family for the first time since his parents and sister died in a fire when he was a child. He stopped by for one last tearful goodbye. “I’m going to miss my family at 51 like hell,” he told a big group of his former colleagues. They soon walked away, leaving only Blake’s best friends, Darren Ritter (Daniel Kyri) and Violet Mikami (Hanako Greensmith).

“Oh, you guys don’t know: I already made two new best friends in Detroit, Riolet and Vitter,” Blake joked, as the three of them teared up and hugged. Before heading out on a call, Violet gave Blake one last kiss on the cheek. Despite saying goodbye to her former love interest and preparing to bid her ambulance partner Sylvie adieu, Violet appeared to be saying hello to someone else: She and Sam Carver (Jake Lockett) had a few little moments that implied they may be keeping a romantic secret. (Ha. A secret at Firehouse 51? We’ll see.)

Toward the end of the episode, Chief Wallace Boden (Eamonn Walker) and Christopher Herrmann (David Eigenberg) caught the arsonist dropping off a package at 51. As Boden apprehended the guy, Christopher ran the explosive into the park across the street. As it detonated, Christopher was thrown against the ground hard. He insisted he was fine as Violet and co. ran to his side, but something about the way he was sitting in the locker room at the end of the episode wasn’t quite right… And in the teaser for next week’s episode, Joe Cruz (Joe Miñoso) is struggling to take orders after he served as the team’s leader while Kelly was away — and threatens to leave Firehouse 51.