The second season opens with Severide being targeted by an arsonist. Meanwhile, Chief Boden goes up against a high-ranking consultant who is considering closing Firehouse 51; Casey remembers Andy on the one-year anniversary of his death; Shay wonders about Severide's paternity; and Mouch's Japanese girlfriend visits.
Casey struggles with the effects of Heather's accident; Severide anticipates the next attack from the firehouse's arsonist and goes to Renee about his paternity suspicions; Mouch campaigns for union president; and Shay and Dawson want to get out.
Severide seeks proof to confirm his suspicions about the arsonist's identity; Casey gets used to his new lifestyle; Molly's bar is in trouble; Dawson goes on a date; and Mouch's campaign takes off with the help of an old friend.
Severide wants to charge the serial arsonist; Dawson and Shay get a surprise during a routine call; Clarke is suspected of being the mole inside the firehouse; Molly's bar continues to have financial trouble; Mouch campaigns for union president; and Boden goes up against Gail McLeod.
Boden's future with the firehouse is in jeopardy when McLeod pushes him toward an early retirement and finds a potential replacement for him. Meanwhile, the mole's identity becomes clear; Shay's social life picks up; and Arthur takes money from Molly's.
Severide goes out on a jog and discovers a young boy trapped inside a backhoe loader at an abandoned construction site. Meanwhile, Boden and McLeod argue about the future of the firehouse; Mouch and Greg Sullivan hold an Election Day debate on Otis' podcast; and Molly's rival is in trouble.
The firehouse squad is on the scene of a major accident involving a tanker and a commuter train that collided and then crashed into a warehouse. Meanwhile, Boden faces big decisions; Severide learns more about the woman he saw with his father; Shay and Dawson are at odds; and Casey experiences a development in his responsibility of being a surrogate father.
Cruz and his brother wrestle with emotions after a young girl is shot in their neighborhood. Meanwhile, the fight between Chief Boden and McLeod gets intense; Isabella tries to get Mills to dress up for a party; Casey is upset that his parental duties have ended; Shay reaches the end of her rope; and Zoya deals with her expiring visa.
Boden makes one last-ditch effort to save the firehouse from being closed; romance blooms between Dawson and Casey; Leon makes progress in the gang-murder investigation; Severide and Katie bond; and Otis feels out of sorts living with Severide and Shay.
Chief Boden and the squad prepare to fight the decision to close Firehouse 51. Meanwhile, danger looms as the team responds to an emergency call at an apartment building; Dawson receives major news; and union president Greg Sullivan makes headlines.
Lt. Casey returns to work; Shay meets her new partner; Dawson begins training at the Chicago Fire Academy; Lt. Severide prepares for his instructor assignment; Clarke refuses to talk to the police; and Molly's future looks bleak.
Casey tries to convince everyone—including himself—that he's fully recovered from his traumatic accident, despite evidence to the contrary. Meanwhile, Shay avoids a lawyer who wants to talk to her about Daryl's suicide; Otis and Katie bond; Boden helps a woman deal with her irresponsible landlord; and Dawson notices something interesting about recruit Rebecca Jones.
The members of Firehouse 51 help out the community after a power outage leaves the neighborhood in darkness on a cold evening. Meanwhile, romances and tempers intensify among the firefighters left at the station during the blackout; Casey continues to hide his condition; and Molly's stakeholders argue about the bar's direction.
Severide feels left out during the search for his missing sister. Meanwhile, Shay gets a surprising tip; Casey gleans new information about his head injury; and Dawson trains for the physical test at the Academy. Chicago Blackhawk players Brent Seabrook and Duncan Keith appear as themselves.
Severide grows frustrated when Vince Keeler goes free, but he maintains hope that justice will prevail. Meanwhile, the firefighters work to rescue a girl trapped inside a donation bin; Mouch learns not to cross Boden's secretary; and the squad responds to a high-rise fire in a downtown office building.
Det. Lindsay narrows down potential suspects in Keeler's disappearance, and Severide's motives place him at the top of her list. Elsewhere, Jones' disruptions are noticed by headquarters; and Hermann and his wife celebrate their 20th anniversary, but his idea for a gift may be ill-advised.
Severide feels moved to help the victim of a car accident because the man reminds him of his own past. Meanwhile, Casey and Boden wonder how they should dock Jones; Mouch and Dawson each deal with opposite-sex problems; and a heroic action has consequences for the squad.
Severide reaches out to a Denver firefighter who's battling an addiction. Meanwhile, Dawson and Shay enjoy a girls' weekend away; Jones learns that her father is putting pressure on Boden about her career; and Mills helps Mouch upgrade his online-dating profile.
As the firehouse staff deals with a tragedy, Dawson receives a suicide note and Severide looks into Bloom's past. Meanwhile, Chief Boden receives distressing news and asks Shay for help finding a crucial item.
Dawson prepares to retake the fireman's exam. Meanwhile, Casey has an important discussion with Antonio; a new addition joins the squad; Shay deals with a surprise guest; and Boden makes a daring move.
A fire breaks out at a boarding school in the Season 2 finale, and Severide questions himself in the aftermath of the blaze. Elsewhere, Dawson retakes the fireman's exam, with some political help from Casey; Mills searches for answers about his father's past; and Boden's plans go awry.