After learning unsettling news, Dawson enlists Severide to help her out. Elsewhere, Casey and Dawson struggle with communication issues while Brett and Kidd compete to win the heart of Zach, a Hazmat officer. Meanwhile, Otis, Herrmann and Mouch are on a mission to locate the source of a horrible stench that is making life unpleasant at Firehouse 51.

Dawson and Casey do everything they can to locate Bria's whereabouts after discovering important new information. Lt. Severide reunites with Chief Grissom, and old family friend. Meanwhile, Cruz enlists the help of Brett and Mouch to create a new tool and Kidd and Zach go on a date.

After responding to a time-sensitive rescue, Casey and Severide don't see eye to eye on the best course of action. Herrmann struggles to entertain his daughter on "bring your child to work day." Brett is joined by a surprise guest during a spa getaway, courtesy of Dawson, while Kidd's social life gets a boost.

After photos of Casey and Severide jumping off the roof during a heroic rescue make the front page of the newspaper, Boden unwillingly agrees for the photographer to chronicle a day-in-the-life story at the Firehouse. Dawson and Brett are on a mission to find out what keeps happening to Gerald, a frequent flier they know who lives on the streets. Meanwhile, Herrmann decides to take up life-coaching as a side job and Kidd makes a decision regarding her living arrangement with Severide.

While working to track down a bombing suspect, Voight and Antonio meet with Chief Boden, who unwillingly agrees to let Dawson and Brett go undercover. As the investigation continues, Boden, Casey and Severide lend their skilled expertise in the investigation. Elsewhere, Kidd and Zach's relationship hits a bump and Cruz has a hard time expressing his true feelings for Brett. Meanwhile, Herrmann and Connie are forced to come up with an alternative solution when two birthday parties are booked on the same day at the firehouse.

The crossover starts on Chicago Fire S05E016 Profiles (I).