Now the sole caretaker for the Darden boys, Casey strains to juggle Griffin and Ben with his firehouse duties, a conflict that peaks when the school calls him while he's on duty. With Boden's blessing, he sneaks away, only to find out Griffin punched a classmate and now faces detention. The principal and Casey butt heads over Casey's parenting skills - until Dawson shows up masquerading as his girlfriend. She puts the principal at ease and later brags to Shay about her lack of nerves. Maybe she really does like Jay...
At the firehouse, news spreads that Severide and Shay need a roommate at their new place, and two suitors decide to compete for the opportunity: Otis and Cruz. They agree to take the cinnamon challenge - swallowing a spoonful of ground cinnamon in under 60 seconds without drinking anything - to determine the best man. While they sort out the details, Severide ushers his dad into Boden's office, and the three men chat about the suspected arsonist, Hadley.
Benny makes a solid argument for the ex-fireman's involvement, and Boden reluctantly allows the investigation to continue - a decision he regrets when McLeod visits him (as always) unannounced. Word travelled fast about Arson opening up a case against Hadley, and she wants all the details about his unceremonious exit from Firehouse 51. Boden tries his best, but somehow she makes him into the bad guy.
After a daring underwater rescue, the squad unwinds at Molly's, where Herrmann presents a free beer tasting on the patio. This nets a crowd - until CPD strolls by based on a neighborly tip and shuts down the event for violating happy hour laws. Herrmann has a good idea about which neighbor contacted police - Game Day.
Dawson introduces Mouch to her friend Isabella, a strategist with real campaign experience who agrees to help land Mouch much-needed signatures to secure his candidacy. She also catches the eye of one admirer in particular - Mills - but the moment fades once he spots his old flame Dawson getting cozy with Jay.
None of this stops Cruz from continuing to flirt with Otis' cousin Zoya - and he promises her a mix CD the next time they see each other. But when the bar closes down, Dawson and Jay are the last two standing. And Dawson asks for his help cleaning up - after they make love.
The next day, Boden enters the common room with the latest set of McLeod-approved marching orders - all time away from the firehouse must now be preapproved. The house grumbles in response, but Boden's not done - he also rips into Otis over the cinnamon challenge. Afterwards, Herrmann's suspicions boil over and he flat-out accuses Clarke of being a rat.
Another 51 suspect strides over to interrupt the tensions - Hadley. He goes chest-to-chest with Severide and warns Clarke about trusting anyone at the station. The alarm sounds and ends the skirmish, but it restarts when Hadley follows them to the scene of yet another dangerous building fire. Severide struggles to contain his emotions even as Hadley makes an inconvenient observation - how could he be behind the fire when he was at the station when it started?
Later, Casey takes the boys on an emotional visit to their mom in prison and afterwards learns the true nature of Griffin's discontent - he wants Casey to promise he won't leave them like his mom and dad. Casey assures both boys that they can count on him.
Back at Molly's, Otis anonymously reports a fire code violation at Game Day, redirecting their customers to Molly's and packing the bar. Cruz feeds off the jubilation and hands Zoya the mix CD he promised. She thanks him and hops into a car - with Severide!
Totally devastated, Cruz pulls out of the roommate competition as a result, a move that's immediately usurped by Mouch solidifying his 200th signature - he's officially on the ballot! All thanks to Isabella's social media know-how. To Mills' surprise, she saddles up to him and asks if he'd like to celebrate.
But just as things are looking up, Arthur, the wannabe mobster, stops by looking for his cut of the bar and wanting to revise their silent partnership for more cash. When Herrmann and Dawson refuse, Arthur mentions he knows all about their expenses and their profits - he has a spy on the job. And it's Jay.