Firehouse 51 responded to a horrific warehouse fire that killed 39 people. This led the Chicago P.D. on a manhunt for the suspect. Now with someone in custody for both arson and multiple murders, it is up to Peter Stone and his team, including lead investigator Antonio Dawson to step in to bring some peace and resolution to so many families and friends of those lost - including one very close to home.

The crossover starts on Chicago Fire S05E15 Deathtrap (I) and Chicago P.D. S04E016 Emotional Proximity (II).

When a Muslim grad student is brutally murdered, Stone and the team arrest his friend, another Muslim student, who claims he committed murder to prevent a terrorist attack. The jury must decide whether he's a killer or a hero.

When a pregnant woman is found murdered and her baby cut out of her, the State's Attorney's Investigators race to find the baby and the killer. The case is complicated when it's revealed that the killer's DNA matches that of her father: a convicted serial killer already in prison. Both killers then attempt to use the DNA evidence as their ticket to freedom.

When Abigail Chapman returns from Spain after being acquitted for murdering her boyfriend while studying abroad, she finds herself the prime suspect in another murder case involving a young college student. During the trial of the real killer, the Second Amendment is put to the test.