During a harrowing call to a structure fire, Herrmann rescues a trapped toddler, but the questionable circumstances surrounding the event sends him on a personal mission to locate the father and get to the bottom of the situation. Severide makes up for lost time by retracing key friendships from his adolescence, while Mills discovers some surprising news. Elsewhere, Cruz and Brett's relationship comes to a crucial juncture, while Otis develops some unexpected feelings.