Severide accosts the recently released main suspect in Katie's kidnapping, Keeler, outside District 21. How can P.D. let him go when it's clear he orchestrated the whole thing? Detective Lindsay attempts to calm him down by explaining that they've got Keeler bugged; this is all for the better. But that doesn't impress Severide, who goes rogue and muscles through two contacts for info on Katie's whereabouts, beating one guy senseless before he reveals the address to a warehouse. He and Lindsay bust through it to find Katie - beaten, bruised, terrified, but alive.
Meanwhile, Dawson once again fails to finish an obstacle course in the required time to graduate from training. Her frustration doubles at her fellow trainee's success: Jones whips through the trials with ease, a total natural. When the final trial arrives, Dawson pushes herself hard, but cracks her ankle on a staircase and drags herself across the finish line... seconds too late. She doesn't pass.
But Dawson's not the only one getting tested. Casey's medical exam comes back with troubling results. The doctor explains that any additional trauma to his cracked skull could have serious repercussions, a detail that ultimately causes him to come clean with Dawson. She accepts his apology - and his promise to tell her the hardest truths.
With firehouse tensions high due to Katie's kidnapping, Boden agrees to a welcomed dinner with Donna and a few of her friends. His past becomes a conversation and he acknowledges his two divorces and estranged stepson, Jimmy. This weighs heavy on his mind later - is he doomed to failed relationships? - and leads Boden to end things with Donna. She feels differently, but respects his decision.
After Rafferty and Shay save a devout man's life by administering emergency medication he initially refuses, the man files a high-level complaint. This results in Rafferty being hit with a suspension. The shock notwithstanding, the two once-prickly EMTs share a tender moment; they've come a long way. But there's a silver lining to Rafferty's sudden exit - she recommends Dawson as her replacement.
Later, Lindsay contacts Severide to observe while she and Antonio surprise Keeler with an arrest. Keeler's capture spurs Severide to join Katie in the hospital where she reveals the bittersweet news Otis already knows: she's moving to Colorado. Although he's sad to see her leave, Severide agrees it's the best thing for her after the kidnapping.
Between Katie's rescue, Dawson's failed test and Boden's breakup, all of 51 rallies around a feel-good moment: the unveiling of the firehouse's gift to the neighborhood, a new library dedicated to Nathan, the kid who helped raise funds during 51's near-closure. All the firefighters celebrate the day at Molly's, where Shay auctions off center-ice Chicago Blackhawks tickets from two unlikely sources - Brent Seabrook and Duncan Keith, actual Blackhawks (and Clarke's friends)! Herrmann adds to the cacophony with an announcement of his own - he finally passed the lieutenant's test. But the happy news takes a sour turn for Dawson when Jones steps over to Casey and introduces herself... as the new candidate on Truck 81. She's joining the firehouse.
Conspicuously missing from all this is Severide, called into District 21 by Lindsay. Turns out Keeler's got contacts that go high up and P.D. has to release him. Severide's blood boils at the mere suggestion - but Lindsay's hands are tied...