"The Bad Guy" is a change of pace from the episode that preceded it. "Cut Me Open" may sound morbid on the surface, but the Chicago Fire story revolved around the personal lives of two of its most beloved characters: Stella Kidd (Miranda Rae Mayo) and Kelly Severide (Taylor Kinney).
"The Bad Guy," on the other hand, is an investigation into the professional life of one Dom Pascal (Dermot Mulroney), and the crime he may have committed using CFD tools. SPOILERS ahead!
The episode kicked off with some general 51 housekeeping. Kidd and Severide discussed how saddened they are by the fact that they didn't become parents, and how they wanted to focus on work in the meantime. Then there was Herrmann (David Eigenberg), who made quite the awkward discovery as he was preparing to take his chief exam.
Apparently, Herrmann needs a recommendation from his chief before he can officially take the exam. Seems easy enough, except for the fact that his chief, Dom Pascal, is the guy he's angling to replace at 51. These two have developed an uneasy relationship over the course of season 13, and based on this latest discovery, it is not going to get any easier.
Pascal is suspected of attempted murder

Speaking of Pascal, let's get to the main event. Firehouse 51 is called to the scene of a car accident, and sure enough, the man behind the wheel is the man who was involved in the death of Pascal's wife, Monica (KaDee Strickland). The coincidence is not lost on the firefighters, especially Severide, who ascertained from witnesses that the fire in the car started before the man crashed.
Severide did his arson investigation thing (always nice to see), and even conferred with Van Meter (Tim Hopper), the mean who nearly stole Severide away from 51 to become an investigator full time. The character discovered that the fuel line on the man's car was cut, making the accident attempted murder. He withheld the Pascal connection from Van Meter, however, and confronted the chief about his findings first.
Pascal insisted that he was home the night the fuel line was cut, but he was alone so Severide had no way of corroborating his story. Severide told the chief OFI was going to need a much stronger alibi if he was going to be cleared of suspicion. Pascal's alibi looked even flimsier when Captain Van Meter discovered a tool belonging to the Chicago Fire Department in the victim's car.
Kidd was convinced that Pascal was guilty. She was also occupied with the reappearance of Natalie Evans (Eva Torres), a teenager who she saved some ten years ago. Natalie told the firefighter that her older sister wanted her out the house, but her mother lived all the way in St. Louis. Kidd's burgeoning maternal instincts kick in, and the two traveled to St. Louis to solve the problem.
Stella Kidd bonds with a motherless teen

Tragically, Natalie learned that her mother moved without telling her. The teenager headed back to Chicago, heartbroken, with Kidd. We can't imagine we were alone in thinking that the Chicago Fire writers are setting up a season 13 finale in which Kidd and Severide adopt Natalie? Right?! All the signs point to this happening soon.
Let's get back to Pascal, though. Severide wasn't as convinced that the chief was guilty, and he did some digging into Pascal's past. Finally, the Miami backstory came into play after a season of laying dormant. It turned out Pascal used to work for a man named Hendricks, who did business with the mob. The chief knew it was going on, and told Severide that he did it for the benefit of his wife.
We got a flashback, a rarity in Chicago Fire, which revealed that Pascal was actually working to take Hendricks down, but his decision to abandon the investigation and move to the Windy City with his wife not only made him seem complicit in Hendricks' actions, but opened him up to retaliation. One doesn't mess with the mob and get away with it. Unfortunately, the flashback did nothing to help in the present.
"The Bad Guy" concluded with Pascal being taken into custody. Van Meter made his frustration with Severide, who kept information from him throughout the investigation, clear, suggesting both Pascal and Severide could suffer repercussions come the season 13 finale. Yikes.
Herrmann's quest to become 51 chief may have just gotten easier.