Dawson blasts through the firefighter's test, pushes herself to cross the finish line - and passes! The celebration only lasts until Boden announces her new station - Firehouse 105, headed by the mean-spirited Welch and his unwelcoming squad. This annoys Casey more than Dawson, and he confronts Welch, who bluntly states that Dawson is a token firefighter and will be treated as such. Casey responds by orchestrating a transfer to a firehouse in Logan Square - but Dawson rejects it. She wants to be treated like every other candidate and promises Welch won't break her.
A call sends 51 to a burning boarding school, several stories high, and they sweep every floor for victims. They rescue several kids mostly unharmed, but it's not until they put the fire out that they discover a charred body from one of the rooms Severide cleared. The oversight devastates Severide even though the victim manages to survive. Severide attempts to distract himself from the pain by working on a motorcycle at 51, and when that fails, he visits the burn victim at the hospital. Although he never meets the young boy, the moment makes him emotional, and Severide returns to the apartment to find Devon, the last person he wants to see, and lays into her, livid about her return. Severide leaves right as Shay arrives, and he seeks out Lindsay afterwards. She provides a willing ear and the two confide in each other, sharing stories about regret.
Meanwhile, Boden and Donna decide to marry right away, and the chief enlists Herrmann as his best man. Elated, Herrmann promises a full ceremony at his church St. Ignatius... except when he makes the call to the church, the priest denies his request. The news deflates Herrmann, and he avoids telling Boden until the last minute when he rearranges everything and surprises the chief with a full ceremony at the firehouse. Mills officiates and the whole squad stands by as Donna and Boden exchange vows. It's a beautiful and touching affair.
Love remains in the air, as Mouch appears to make a connection with an unlikely single - Sergeant Platt from P.D. While they flirt, Casey seizes the moment and proposes to Dawson, but before Dawson can answer out loud, the alarm sounds. Boden, still in his tux, joins the squad on the call to what looks like a minor fire at a five-story building. Dawson and Shay follow the rest of the squad inside, and as usual, the chief stays back. But then he loses radio contact, and suddenly the silence feels eerie. What's going on? The radio crackles with Severide issuing a pull back warning, and before Boden can gather the gist - the building explodes! All the windows blow out and smoke fills the sky. Boden screams into the radio, calling for anyone on his team...
But no one responds.