Season 3 Episode 17
"Forty-Caliber Bread Crumb"
When Halstead becomes the victim of a brutal off-duty robbery, all of District 21 joins in solving the case.
While out on a bank run for his off-duty security job at a dispensary, Halstead (Jesse Lee Soffer) and his co-workers come under attack by a violent robbery crew. One of Halstead's friends is killed in the ensuing shoot-out, leaving a shaken Halstead out for vengeance. Voight (Jason Beghe) and Lindsay (Sophia Bush) question the owner of the dispensary, who mentions that she has received threats from local gangs who are upset that the collective is cutting into their business. Burgess (Marina Squerciati) and Roman (Brian Geraghty) are detailed to the unit to help explore all leads. After an investigation that points the team in several different directions - including the ex-husband of the collective's owner - Intelligence discovers that a private detective had learned of the cash drops, and was responsible for putting the robbery in motion. After Intelligence engages in a deadly shoot-out with the crew behind the heist, the criminals are brought to justice. Halstead decides to quit the security job, after which he and Lindsay make an appearance at his friend's military funeral, which Halstead attends in his Army Ranger uniform.