More clues surface surrounding the fire that killed Shay, leading Severide to a most unexpected source who may be able to provide pertinent information. Meanwhile, Shay's sister Megan comes to town, prompting members of the firehouse to remember Shay's life. Elsewhere, Cruz is in for a surprise when Otis's grandmother moves into their apartment, while Boden finds a way to help his dying father make the most of his last few weeks.

Interim Chief Pat Pidgen is brought over to temporarily fill in for Boden, who is left to tend to his personal affairs. When tension is sparked as the result of his derisive leadership, the absence of Chief Boden becomes all too apparent. Meanwhile, Lieutenant Severide must deal with a most unwelcome addition to his squad, Brett gets closer to a girl she previously rescued and Casey starts seeing a new woman, Beth, but interesting complications quickly unfold.