Chicago Fire - Season 5 Episode 12
An Agent of the Machine

The team is on high alert when a previous incident during a fire call leaves a dangerous man on the loose with a vendetta to target Lt. Casey and Firehouse 51, and prompts CPD to step in. Dennis Mack, a buddy firefighter of Severides father, comes to town to shadow the squad but may have ulterior motives. Meanwhile, Brett and Antonios relationship hits some bumps in the road when his ex-wife Laura surfaces and Casey has a present for Dawson.