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'Chicago Fire' season 5 episode 12 spoilers: Dangerous man puts team on high alert; Antonio's ex-wife returns

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A dangerous criminal targets Firehouse 51 on the upcoming episode of "Chicago Fire" season 5.

Titled "An Agent of the Machine," the show's next episode will see the responders on high alert. According to the official synopsis, the team is worried about their security when a previous incident during a fire call leaves a dangerous man on the loose. He plans to target Lt. Casey (Jesse Spencer) and Firehouse 51, forcing Chicago P.D. to step in and investigate. Dennis Mack (guest star Nick Boraine), a firefighter friend of Severide's (Taylor Kinney) father, heads to the Windy City to help the squad out. However, he may have ulterior motives that could further complicate the firehouse's situation.

Meanwhile, Casey surprises Dawson (Monica Raymund) with a special present, while a familiar face from Antonio's (guest star Jon Seda) past resurfaces. His relationship with Brett (Kara Killmer) hits some bumps in the road when his ex-wife, Laura (guest star America Olivo), comes to town.

NBC recently released a new promo clip for the episode, and it gives a preview on why Firehouse 51 was attacked. "An attack on the firehouse is completely personal," the background voice says. It turns out that a man believes he was left by the firefighters to die during a past fire incident. He managed to survive and is now out to get revenge on the responders for not rescuing him.

Back in December, it was announced that Laura will return to Chicago to see her former husband. Although this episode marks her first appearance on "Chicago Fire," the character is certainly no stranger to the Chicago universe. She has been in six episodes of the spinoff procedural "Chicago P.D." early in the series run. At the time, she was still happily married with Antonio as she takes care of their two children. Laura decided to end their relationship and file for divorce at the end of season 1.

The fifth season of "Chicago Fire" airs every Tuesday night at 10 p.m. ET on NBC.