Lt. Casey (Jesse Spencer) and Dawson (Monica Raymund) apply for permanent adoption of Louie, but quickly discover a hurdle. Firefighter turned medical student Jeff Clarke (guests star Jeff Hephner) approaches Lt. Severide (Taylor Kinney) with an interesting proposition. With hopes of reinvigorating business at the bar, Otis convinces a skeptical Herrmann to throw a bash in celebration of the milestone 100th anniversary of Molly's, but not without complications.