Lindsay rushes into Annie's apartment to find her friend bleeding from a bout with Charlie, who's irate about Annie shutting him out of their son's life. He calms down long enough to negotiate with Lindsay: he will stay mum about a certain secret of theirs if she can come through with blueprints to a jewelry exchange. She obliges and keeps the breach a secret from Voight.
Back at District 21, Antonio returns from the hospital looking to jump back into casework, but Voight relegates him to desk duty until he fully recovers. Voight's not the only one concerned about a premature return, though - Antonio's wife calls to complain and the two entangle themselves in a serious argument.
The squad - including Atwater, the latest addition - focuses its energy on a construction site that reports stolen water gel explosives... and leads Intelligence to a dead body. Halstead and Ruzek use an informant to set up a meeting with a new player in town, someone rumored to have a connection to the murder. Unfortunately for them, that person is Charlie, who stalls the investigation once he recognizes Halstead. To protect Lindsay, Halstead and Ruzek hold back on relaying the information to Voight and instead support Atwater on an undercover sting that secures their next piece of intel - the man behind the murder is Red Radner, a dangerous criminal... with ties to Charlie.
Still on edge from the rift with his wife, Antonio rallies for a civilian aide in the office. The perfect possibility comes into play when Lindsay requests Antonio pick up Nadia from the clinic. Now that she's sober, she needs a job. But can she hack it?
With Halstead's encouragement, Lindsay comes clean to Voight and the team arrests Charlie moments before he knocks off the jewelry exchange. As they slap on the cuffs, he reports a murder from 2002 - one that implicates both Annie and Lindsay. But Lindsay appeals to his future with his son and Charlie recants - and gives up Red Radner's location, a warehouse in "B.Y." No one on the squad has ever heard of B.Y. and suddenly the case looks dead in the water again... until Nadia pipes up. Her streetwise knowledge pinpoints the area, but when Intelligence hones in, Radner's goons ID them as cops. A wild car chase ensues with both groups firing at each other - until Radner's van upends. Halstead detains the driver, but Radner sneaks behind the detective with gun raised. When Lindsay reacts with shots of her own, Radner goes down and Halstead nods his thanks to her.
Jin steals a moment away from the district to meet with Stillwell, who continues to rally for more specific intel on Voight, once again dangling Jin's father as motivation. To make matters worse, seconds later Jin's confronted by a more imposing man - Voight. He followed Jin and knows about the link to Stillwell. He roughs him up a little, but lets him go... only to meet up with Stillwell later for their first exchange. Stillwell accepts $10,000 from Voight and the two officially enter into an off-the-books partnership. Jin, on the other hand, scrambles at his desk and copies information onto a thumb drive that he packages in the mail. He also instructs his father to leave Chicago immediately...
Meanwhile, Burgess languishes away with a new, disinterested partner who refuses to recognize a burglary in progress, forcing Burgess to arrest the perpetrator herself. Platt promises to reassign a new officer and, for once, gives Burgess some encouragement. Later, at her apartment, someone else comes by for support - Ruzek. What starts with a sincere apology escalates into a kiss... and then to the bedroom.
Things aren't as rosy for Antonio after shift, though. He finds his house quiet and empty, no sign of his wife or Diego, with one exception - a note. He tears up as he reads it... did his loyalty to Intelligence destroy his marriage?
But even more serious is the next revelation between Voight and Stillwell. The two end up outside of town - a familiar place for Voight, the same spot he's taken criminals before. Only now they're surrounded by cops, all standing over a dead body...
The dead body of Sheldon Jin.