A dangerous man is on the loose with a vendetta against Lt. Casey and the Firehouse 51 squad; Antonio's ex-wife appears; Casey has a gift for Dawson.
Citing a need for improvement, Chief Anderson reassigns members of 51 to other firehouses, leaving the crew members to make the best of their respective new situations; Severide struggles with an important decision.
Chief Anderson feels his authority was undercut after Chief Boden makes a decision that overrides Anderson's when both squads respond to the scene of a dangerous accident; Severide ponders a lifechanging decision; Herrmann does a good deed.
The discovery of two dead bodies in a forest leads the NCIS team into the wild world of modern-day treasure hunting; Gibbs and Fornell get deeper into their search for the opioid kingpin.
Gibbs and Fornell's crusade to find the head of the drug ring responsible for Fornell's daughter Emily's overdose comes to a climax; Gibbs and Vance finally let the team in on a case that has dangerous implications.