Chicago PD starts with Intelligence planning a drug bust with a big player. They plan to get him and flip him, but when Upton sees him, she tells everyone to stand down.
She ID's the man as Kelly Tyler, a fellow cop and 11-year veteran.
Voight suggests that maybe he was working a case also and their wires were crossed, but all evidence suggests to him being a dirty cop.
Intelligence breaks into Tyler's storage unit and finds confirmation that he's dealing drugs.
A little digging into his files reveals that he's been stealing dope that was supposed to go to the burner with the help of a man named Gibbs, who was signing the orders for the drugs.
They follow Tyler to see who else he's working with and are shocked to see him meet up with Darius Walker, Voight's CI.
Voight confronts Darius who informs him he's been working with the men for 4 years.
He tells Darius that he needs him to work this case, and Darius agrees under one condition: he no longer has to work for Voight.
Voight gets interim Mayor Crawford to sign off on it and the unit begins to hatch a plan.
Platt delivers the fake drugs to Gibbs to "burn."
Darius requests a larger sum of drugs during the buy, which lures out the "big boss," Lt. Mike Packer.
Following the exchange, they test the drugs Tyler and Packer deliver and get confirmation that they're the same drugs Platt handed over thus proving that they've been stealing them.
Voight takes all his evidence to a prosecutor, but Elena doesn't think his case is airtight.
She refuses to give him warrants unless he hands over the name of his CI.
Voight reluctantly agrees and then meets with Darius to let him know that he might have to testify publicly.
Intelligence plans to arrest all the men using the warrants, but when they get to the warehouse, it looks like a warzone.
All three cops involved have been murderer.
Crawford says that to keep the peace, the officers will be hailed as heroes.
Meanwhile, Darius gets to walk free.
Voight even meets up with Darius who admits to having his men for the ambush without actually admitting it.
Upton isn't pleased with the outcome considering her issues with Darius. He killed her CI, Cameron.
She pays Darius' men a little visit and tells them that he was a snitch.
The next day, Darius' body is found on a pool hall with a rat hanging above him.
Upton is pleased with herself. Voight has a chat with her about doing things that you can't go back from, but she doesn't seem to feel any remorse for her actions.