The kidnappers give Antonio an ultimatum - release Pulpo by midnight, or his son Diego dies. The unit only has one play in the interim, a midlevel climber named Ernesto with eyes on a spot in Pulpo's gang. They stake out an old address, and he shows - but Ruzek makes a dumb play, and Ernesto skirts the trap, assaulting Lindsay in the process. Antonio fumes at the wasted opportunity until Jin passes on new info - a live stream from the kidnappers with Diego tied to a chair. Pressure mounting, Antonio makes a private suggestion to Voight - what if they make the deal with Pulpo's men?
Antonio contacts his most reliable informant, Janice, and taps her for knowledge. She digs up intel that sends the unit to a dingy hotel - and an empty room. Right as Antonio finds evidence that proves Diego was there, Ernesto appears in the hallway. After a quick chase, they corner him in the alley where Voight hands Antonio a knife - he's got two minutes before uniforms flood the alley. Antonio nearly gives in to the urge to torture Ernesto, but relents at the last second.
Back at the station, Ernesto refuses to answer questions without a lawyer, a move that sends Antonio into a spiral and stalls the case wholesale. His wife Laura pulls him aside and appeals to him as Diego's mother - get their son back by any means. Moments later, Voight cuffs Ernesto to a cage, and he and Antonio beat the truth out using chains like brass knuckles. Ernesto squeals on Diego's kidnapper, Mateo, and a cell trace leads them to Union Station - and his discarded phone in the trash. The team fans out. Lindsay spots Diego and Mateo boarding a bus headed for Indianapolis.
Against Voight's orders, she follows them on, alerting via text that Diego's unharmed. The team arranges for the bus driver to fake engine trouble and stop for repair, buying time for Olinsky and Ruzek to pose as drivers on the backup bus. Everything goes to plan - except Mateo sniffs it out and pulls a gun. Lindsay does the same - it's a standoff in the bus, with no visibility for a snipe from Halstead. Always thinking on his feet (for better or worse), Ruzek runs to the backup bus and rams the back of the "broken" one. The crash sends Mateo to the ground and Diego into Lindsay's arms. Just as Mateo regains his balance, gun still raised, Antonio leaps onto the bus and fires into Mateo's chest, an instant kill.
The next day, the team reconvenes in their dress blues at the cemetery for the funeral of deceased detective Julie Willhite. This event - coupled with Diego's retrieval - reinvigorates Voight's cause, and District 21's commander admits as much, allowing Voight to run the Intelligence Unit "his way." Later, on the outskirts of town, Voight meets with a woman from Internal Affairs, livid at his recent inaction on supplying her with heavy hitters in the city. They have a deal - he acts as a pipeline to high-end criminals, and she keeps him out of prison. Voight laughs it off - she'll get names on his time.