After a van explodes during a Chicago street festival, a Muslim patrol officer Frank Toma goes missing and evidence quickly piles up pointing to his involvement. Burgess - who helped train Toma - is desperate to prove his innocence, even if that means going against her superiors.

When a gang from El Salvador infiltrates Chicago, Intelligence works with a visiting detective to put an end to the crew's brutal tactics. Meanwhile, Antonio finds himself getting close to Salvadoran Detective Marcella Gomez and Voight learns that the body of his son's killer has been found.

A string of stash house robberies lead back to an unlikely individual. Voight confronts a key witness in the Bingham investigation.