Severide and Stella are on the lookout for her unstable ex.

Members of 51 end up in a dangerous situation while responding to an auto accident and Stella must make a serious decision about her ex.

Casey gets help from Susan Weller for an urgent personal matter; Severide is given an opportunity to travel with Travis Brenner; Stella saves a street kid from a tunnel fire.

Casey is forced to take extreme measures when a forklift accidentally pierces a tank of acid, causing it to spill and putting a father and daughter in danger.

Casey and Severide disagree on a potential arson case when the squad fails to save a woman from her burning house.

Dawson hits a pedestrian while responding to a call. Casey and Severide continue to investigate an arson case while Chief Boden is in New York to attend an important function.

Gabriela and Antonio's parents come to Chicago for their anniversary, while Chief Boden discovers a secret about his stepson.

Casey and Dawson apply for permanent adoption of Louie. Jeff Clarke gives Severide an interesting proposition. Otis convinces Herrmann to throw a bash celebrating the 100th anniversary of Molly's, but there are complications.

Dawson and Casey meet Louie's biological father. In other events, Severide falls back into old habits as he tries to help Anna with a bone marrow procedure, and Brett opens up to Dawson.

Dawson tries to keep her emotions in check during an ambo run involving a pregnant teenager, while Casey is forced to make a split-second decision regarding two victims in need of assistance and deal with the repercussions.

A superior comes after Boden for making a split-second decision in an accident that overrides him.

Members of Firehouse 51 are split up and reassigned to various houses in Chicago by Chief Anderson.

Firehouse 51 responds to the scene of a blaze that puts many lives in danger, including someone related to a Chicago police officer.

Firehouse 51 is taken over by local gangsters.

When similar car accidents uncover the fact that someone may be targeting innocent people, a determined Dawson takes matters into her own hands to help push things along, meanwhile Casey tends to his Alderman's duties.

Dawson and Brett have a new trainee assigned for their shift; Severide's father pays him an unexpected visit.

Casey is reunited with an old colleague when the squad's rig breaks down in the field.

Casey takes drastic measures to help Kannell.

Cruz faces a possible suspension from the fire department for an off-duty incident.

A dangerous warehouse fire puts truck and squad at risk. Tensions rise for Dawson and Casey as Dawson's father overstays his welcome at their home. Mouch considers retirement.