Dawson helps Casey clean up the guest room where the Darden boys stayed. They both agree it's a bittersweet affair and Casey expresses an interest in the two of them hanging out alone - she's been such a huge help, after all - but Dawson pushes back. She reminds him they've been down that road before...
Across town, Cruz and his brother, Leon, enjoy a walk together in their neighborhood when shots ring out - leaving a young girl, Yvette, lying motionless in the wake of drive-by. Chicago PD detectives Voight and Lindsay come on the scene and assure Cruz they'll find the shooter. Cold comfort, considering Voight's past with Firehouse 51.
At Severide and Shay's apartment, Otis finally bonds with Devon over an unlikely source - nerdy memorabilia. Her ears perk up at the value of a Battlestar Galactica helmet, but Otis hears something bigger - Shay's announcement that she requested a transfer, effective immediately. He and Severide can't believe it and neither can the station. That is, until Boden trots out Shay's eager rookie replacement, Alan Chout. His presence trumps even more sad news - Zoya's moving back to Russia. Cruz appears just as hurt as Otis.
Boden returns to his office to find McLeod waiting. She confronts him about his refusal to step down and not only guarantees him that 51 will close, but she promises to bury Boden - it's the kind of thing she lives for. Desperate for a solution, Boden enlists Mouch to solicit help from their last resort, recently elected union president Sullivan.
Mouch visits his old foe and asks for his help with 51's fight. Sullivan refuses to lend a hand - until Mouch threatens to expose an illicit affair. Eventually Sullivan relents and issues an injunction against McLeod - a temporary victory for the station.
A major traffic accident tests Chout's mettle and he fails, hesitating at the wrong time while Dawson and Casey narrowly escape a life-threatening blaze. Chout's personality grates on Dawson again later, when she saves a stabbing victim using household items. All this forces her to think about Shay and, guilt-ridden about the transfer, Dawson seeks out Casey for advice. He reassures her, then makes a confession of his own - he doesn't know what he'd do without her. Dawson chooses not to dismiss the compliment.
After Isabella convinces him to attend a black tie event, Mills arrives in a tux and relishes the opportunity to reconnect. But she throws him a curveball when she introduces Mills as her boyfriend - to an African American senator. When Mills accuses her of using him as leverage to join the senator's campaign, Isabella swears the move was innocent. Either way, Mills takes a cab home alone.
To Casey's chagrin, Voight swings by the station to speak with Cruz about the shooting. CPD knows local gang Insane Kings is behind it but needs someone on the inside to break the case - someone like Cruz's brother (and ex-gang member) Leon. Cruz rebuffs him until Voight links Leon to a suspicious fire and the unsolved death of a gang leader. Detective Lindsay goes even further - Yvette, the young girl, died in the hospital. Cruz is left with no choice but to have his brother infiltrate back into the gang.
Severide meets up with his newfound half-sister Katie - a culinary student with big dreams. Charmed, he asks if she'll cook a meal for the station. She agrees and appears excited, but when she never shows and leaves the station scrounging for lunch, Severide confronts her at the restaurant. Katie apologizes, confessing that Benny disappeared for most of her life and she's not ready to enter into another family "trapdoor." Although Severide understands, he reminds her that he is not his father.
At Molly's, an emotional Cruz drinks away his sorrows. When Zoya joins him and complains about her own future, his tone changes - and he proposes! Sure, it seems impulsive, but this way she can stay in the States and he doesn't have to lose another loved one. Zoya, almost surprised at herself, agrees.
Reeling from Cruz's proposal, Severide and Otis return to their apartment, only to find it in total shambles, all their valuables looted. Severide discovers Shay bawling in her room, alone. Turns out, she gave Devon a key to the apartment. Shay's totally hit rock bottom.
Meanwhile, Dawson sits at home, antsy, almost dialing Casey over and over - should she call him or not? She decides not to and instead puts on a hot dress and heads out the door - where Casey stands, seconds from ringing the bell. They lock eyes and - without saying a word - Casey pulls her close and they kiss...