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Otis and Kidd's lives are put in jeopardy when there's gunfire inside a house; Dawson comforts Brett during an especially trying time; Casey begins to notice that romance might be going on within the firehouse.

The crew struggles to come to terms with an injury to one of their own; a temporary replacement must be dealt with; Boden ponders some interesting news; Kidd has a hard time keeping a secret.

Boden has a lapse in judgment in the aftermath of rescuing a young boy; Kidd struggles to win the approval of Severide's mom after a surprise visit; Otis takes on new responsibilities at the firehouse.

When the FBI takes over the firehouse for an undercover mission, Casey and Severide volunteer to assist with the investigation; Kidd attempts to help Severide come to terms with recent developments he's been managing.

The team responds to a residential fire at a property belonging to a drug cartel; a hefty amount of money is missing from the crime scene; Kidd makes a big decision.

After saving a girl from a car accident, Boden and Severide receive a surprise package; Brett struggles to keep quiet about Cruz reacquainting with his now-married high school sweetheart; a crisis brings Bria back into Dawson's life.

Lt. Severide is shocked when Rene Royce resurfaces; Casey comes up with a plan to help Chief Boden in his latest pursuit; Kidd regrets a decision she made regarding Severide; Herrmann clashes with Lt. Colannino over their son's basketball team.

With Voight sidelined, Antonio and Ruzek clash as Intelligence races to solve a high-stakes case involving a series of overdose deaths caused by bad heroin.

Intelligence joins forces with Firehouse 51 after a devastating high-rise fire is ruled arson, and Halstead, who has a tragic connection to the fire, struggles to stay objective as he gets deeper into the investigation.

Intelligence's investigation into a string of robberies targeting vulnerable immigrants escalates when a teenage girl connected to a critic of the CPD is kidnapped by the robbers.

Burgess finds herself in a difficult situation when she responds to a call while a civilian is in her car for a ride-along that was requested by Brennan.

Intelligence's investigation of a nightclub owner suspected of cocaine distribution is complicated when Ruzek recognizes someone close to him while working undercover.

When the wife of an alderman is beaten to death, Voight finds himself under pressure from Brennan to close the case; Upton shares a dark episode from her past to elicit a confession.