S4, E16: Olinsky's (Elias Koteas) daughter remains in critical condition following a massive fire leaving Intelligence on edge, but more determined than ever to track down the suspect. Voight (Jason Beghe) opens up the case, knowing that he has Stone (guest star Philip Winchester) and his team's full support in the investigation, and all of Firehouse 51 behind him to examine potential origins of the fire. Intelligence works to connect the dots between the building owner, those who were inside, and a string of potential suspects.