Sergeant Hank Voight drags a beaten-up man to a deserted lot outside Chicago. The guy must be guilty of something because he offers Voight cash to let him go - but Voight's not interested. With a gun to the man's head, Voight demands a name. The man squeals on Rev, a drug dealer, and gives his last known whereabouts. Satisfied, Voight instructs him to stay out of Chicago... and takes the cash.
At District 21, Voight joins his elite squad of detectives in the one-month-old Intelligence Unit: Erin Lindsay, Jay Halstead, Alvin Olinsky, Sheldon Jin, Julie Willhite and Antonio Dawson. He reminds them to keep everything they do in-house and leave the rest to him. "You tell me the truth so I can lie for you." They're on board and ready for action.
The team tracks down Rev's apartment with Lindsay and Halstead posing as junkies to get an eye-in on the situation. But Rev doesn't answer and Lindsay suspects the worst when she spots blood. That's enough for Voight and he orders the team inside - except gunfire keeps them at bay and the shooter escapes. Inside they make two discoveries: the decapitated head of their target, Rev, and a witness - a drug runner hidden in the closet, just a kid.
Antonio makes the leap to cartel involvement - beheadings are a cartel signature - and a quick interview with D'Anthony, the kid witness, lands them a name: Pulpo. This guy's already on their radar as a ruthless, Colombian-cartel-trained killer, but they're lost on leads - until Voight visits a sketchy contact who gives up a guy named Coop as a good reference for Pulpo's whereabouts. When they track Coop down, however, it's too late - his chopped-off head sits on the counter. Someone's cleaning house.
Back at the station, acerbic Desk Sergeant Platt gives rookie officer Kim Burgess an errand to retrieve a ring from her dead cousin. It's tricky, but Burgess manages to snag the ring without incident - too bad that's only the first step. Platt instructs her to pawn the ring for $350 "minimum" because her cousin owed her money. Unfortunately, there's a paper trail from Burgess' visit with the ME and she can't pawn it. Before Platt can issue further instructions, Burgess stands up for herself and leaves Platt with the ring - and expecting a call from the ME.
Halstead and Lindsay pull Coop's phone records, which leads to a burner sale in West Town. With a little pressure, the owner gives up the customer: Omar Rojas. The squad goes citywide with images of Rojas and Pulpo while Voight releases D'Anthony from custody. He fears for the kid's safety, but with pressure from higher-ups to let him go, he offers the kid his card. The move pays off fast. D'Anthony calls him for a pickup across town and when Voight arrives, it's clear D'Anthony took a serious beating. He wants out of the drug trade and gives up some new info - there will be one last hit.
With D'Anthony's help, the Intelligence Unit ID's another dealer, Xavier. This marks the perfect opportunity for Olinsky's new academy recruit, Adam Ruzek, to test his mettle and pose as a buyer. Luckily for the squad, Ruzek nails the part and Xavier turns up solid intel on another suspect. The whole unit keys in on the suspect's apartment with Antonio and Willhite running point. Outside, Voight listens in - interrupted by the arrival of Lieutenant Belden from Violent Crimes. They're both surprised - and annoyed, lots of history there - and Voight discovers that Belden failed to share vital knowledge: Belden's team believes Pulpo's in the building!
Right as Voight warns Antonio and Willhite, a gunshot tears through the doorway and Willhite drops, hit in the neck. Lindsay tends to the wound while a fleeing Pulpo gains distance - until Halstead cuts him off in an alley, tackling the assassin to the ground. But the arrest pales in comparison to the loss - Lindsay reports that the wound proved fatal. Willhite's dead.
Charged with anger, Voight bursts into District 21 and accuses Belden of causing Willhite's murder. While Desk Sergeant Platt holds Voight at bay, Antonio interrogates Pulpo in the cage. Pulpo remains antagonistic, confident he has control despite his arrest. Antonio presses, losing his patience - and that's when he gets the news: someone kidnapped his son, Diego.
A grisly beheading sends Chicago's toughest detectives - the newly minted Intelligence Unit - on a hunt for an assassin whose links to the Colombian drug cartel may cost them one of their own.