Chicago P.D. Season 4 Episode 16

Olinsky’s daughter remains in critical condition following a massive fire – leaving Intelligence on edge, but more determined than ever to track down the suspect. Voight opens up the case, knowing that he has Stone and his team’s full support in the investigation, and all of Firehouse 51 behind him to examine potential origins of the fire.

The crossover starts on Chicago Fire S05E15 Deathtrap (I). It continues on Chicago Justice S01E01 Fake (III).