S5, E13: When a gang from El Salvador infiltrates Chicago, Intelligence works with a visiting detective to put an end to the crew's brutal tactics. And Antonio (Jon Seda) finds himself getting close to the Salvadoran Detective, Marcella Gomez (guest star Sofia Lama), only to learn she has a hidden motive for being in Chicago. Meanwhile, Voight (Jason Beghe) learns that the body of his son's killer has been found.