Firehouse 51 is on high alert when a series of explosions rock the city. Herrmann adjusts to his new duties and Kidd gets a visit from an old friend.

Anne Ilonzeh, Anthony Ferraris, Daniel Kyri, Devin Bethea, Jeff Kurysz, Jennifer Weigel, Jerry Kernion, Joey Gilmore, Kaitlin Yamano, LaRoyce Hawkins, Laura Shoop, Mac Rapach, Marina Squerciati, Matthew Abraham, Meg Thalken, Michelle Martinez, Patti Murin, Randy Flagler, Rian Sheehy Kelly, Skye Ellis, Thom Dacey Carr, Tye White