The members of Firehouse 51 struggle to cope when one of their own dies in a fire; as Lts. Casey and Severide blame each other for the tragedy, Casey also secretly goes through a separation.
Severide hides his serious shoulder injury as he tries to rescue a construction worker from a collapsed building; two teens are trapped in a vehicle.
Casey must decide whether to turn in a cop's son who paralyzed a teen in a drunken-driving accident; Severide learns he has a fractured vertebra; Mills is torn between his mother and the job.
Chief Boden faces accusations that he abandoned a homeless man to die in a warehouse fire; Severide helps an elderly woman; Detective Voight tries to convince Casey not to testify against his son; Shay has to face her ex during a call.
Casey must face the consequences of confronting Detective Voight; Dawson faces disciplinary action; Severide reaches out to an old friend about his injury.
Dawson receives help from a girl she saved; Detective Voight is determined to get Casey to retract his statement.
The Firehouse 51 crew has a Thanksgiving to remember when drugs, a car accident, and a gang shooting get in the way of traditional holiday pastimes.
Peter is deeply upset when a young victim is discovered at the site of a train accident; an abusive mother takes dire actions; Severide's injury is aggravated.
Jose Vargas is forced to go on disability after sustaining an injury in a fire; Severide receives a tempting invitation from a woman he saved from a car crash; Cruz tries to end his brother's involvement with a gang.
An expensive necklace goes missing at the scene of a fire, leading to an internal investigation; Cruz makes a desperate decision to save his brother from a gang war; Dawson invites Casey to a party.
Cruz struggles with guilt and decides to make a confession to Casey; Severide asks Dawson for help with his injury; Herrmann is faced with an unpleasant business deal.
Severide finally decides to discuss his injury with Chief Boden; Casey deals with family issues; Dawson responds to a rescue call and realizes a young girl is the only survivor.
A man dies in a fire set by a troubled teenager; Severide contacts his father; Otis fills in for some shifts at the slowest firehouse in the city; Shay and Dawson wind up in a bad situation.
Severide realizes he shares a similar past with the lieutenant who has been helping out at the firehouse; Dawson shares a secret with Shay; Casey faces family issues.
Dawson turns to an unlikely source for assistance as she tries to help her brother; Severide does a favor for Lt. Whaley; Herrmann and Otis make tough discoveries about their silent partner.
Cruz puts himself and his fellow firefighters in danger; Casey tries to resolve issues with his sister and mother; the team assists the bomb squad with a dangerous call.
When Severide's father (Treat Williams) visits, he clashes with Chief Boden over a former colleague's death; Shay makes a decision about Clarice; the mystery about Herrmann, Otis and Dawson's bar is revealed.
Mills questions Bennie about the fire that killed Mills' father; Casey, Severide and Bennie investigate two mysterious diner fires.
A failed rescue attempt deeply affects the men and women of firehouse 51; Dawson and Shay deal with a junkie's crazy behavior during a call; the team upsets local drug dealers.
A paramedic candidate joins Shay and Dawson for a few shifts; Cindy Herrmann experiences pregnancy complications while her husband is out of town; Casey receives an unexpected visit.
Detective Voight shows up, looking to cash in the favor Dawson owes him; Casey's social life takes on a familiar pattern; Molly prepares for the grand opening of Dawson, Herrmann and Otis's bar; Severide faces a threat to his career.
Severide is accused of sexual misconduct; Casey starts to find satisfaction in his personal life; Dawson and Mills face challenges as they try to take their relationship to the next level; the squad faces a harrowing building collapse.
Lt. Casey must work with Voight and the Intelligence Unit; Shay grows increasingly excited about the prospect of motherhood; everyone comes together to support the opening of Molly's.