The episode kicks off with Halstead and Upton on a six-hour stakeout alongside Ruzek and Burgess.
They're waiting to bust a man working for Dante, a gang leader who distributes heroin laced with fentanyl in the city.
When the car-swap happens, Intelligence is confused as to why the other man is taping the driver.
They go after the guy and confront him the drugs, but he informs them that he's working a murder case to find the man responsible for shooting his son, Shawn Wade.
After Intelligence brings him in, Latrell informs them that the police didn't do all that they could to solve the murder, so he took matters into his own hands.
Jay doesn't exactly believe him that his son was a "good kid," but Latrell informs him that he got involved with the Prophets to launch his own investigation.
Jay and Upton reach out to Srgt. Durham to corroborate Latrell's story. He informs them that they "exhausted all credible leads" and found no evidence.
He also tells them that Shawn was in the gang database since he was 14.
Voight and Jay promise to keep Latrell out of jail if he agrees to cooperate and help them take down Dante for the dope.
Jay even informs him that if he helps with the drug case, there's a good chance they will find out who killed Shawn too.
Jay tries to infiltrate Dante's group by buying up some heroin, but when Latrell begins asking too many questions about his car, Dante becomes suspicious and shuts down the deal.
Jay feels bad for Latrell and suggests that since they can't get Dante on the drug charges, they should open up a case into all the unsolved shootings he's connected to.
Jay continues to push the idea that maybe Shawn was a drug dealer or involved with some shady people, but Latrell says it isn't possible.
When he admits to finding two thousand in small bills, Jay is even more convinced that Shawn was dealing and crossed the wrong people.
Jay and Upton confront Travis, the man working Shawn's corner now, but he informs them that Shawn wasn't a drug dealer or a banger.
Instead, he worked at a market on the corner where he was paid in cash under the table, which explains the small bills.
The woman working at the grocery store informs them that Shawn was working there part-time to save up enough money to buy his dad an AC for his garage.
At this point, Jay seems to feel guilty for misjudging.
She informs them that the night of the shooting, Shawn ran out to give his co-worker and crush, Erica Moore, an umbrella to keep her safe from the rain. Erica was dating a well-known gang member, which is who Florence believes killed Shawn.
She explains that she told the police the same thing months ago but a detective from homicide never followed up.
Jay is furious and confronts Durham about never following up on the case.
Durham admits that gang shootings are typically low on the priority list and get swept under the rug after about a week.
Jay and Upton search for Erica, but when they arrive at her house, they see her mom has been injured and the house was trashed.
She admits someone came looking for Erica but doesn't want to get involved.
Voight and Jay pay Dante and his crew a little visit. They accuse him of shooting Shawn since his car was at the scene, but he informs them that he has an alibi for the night of the shooting. And it checks out as there's video surveillance of him at a bar around the time of the shooting.
Erica is brought into questioning. She refuses to talk and says she didn't see anything. She knows it won't bring back Shawn and she doesn't want to ruin her life and her mom's life to make the policy happy.
Intelligence dumps Erica's phone and realizes she was in a relationship with Kayvon Maclaine a.k.a K.Mac. Texts reveal that their relationship was toxic and he was jealous of Shawn. When Dante was out of town, he borrowed his car and found the perfect opportunity to get his revenge.
Latrell comes to the station to talk to Jay, who informs him that they think his son was killed over a girl.
Intelligence deems that they have enough to arrest K.Mac, but when they arrive on the scene, they hear gunshots and find him dead in the alley.
Jay isn't able to stop the shooter.
As he flips through surveillance footage, he realizes the getaway car had a shop receipt on the dash. He visits Latrell's garage and realizes he killed K.Mac.
Jay tells Voight the truth, who informs him that what happens next is solely up to him.
Jay explains that if homicide did their job, Latrell wouldn't even need to seek out revenge and justice.
He confronts Latrell at the shop. He confesses to throwing the gun into the river. Jay tells him to keep his mouth shut and demand a lawyer before arresting him.