Halstead responds to shot's fired at a nearby home and finds a gruesome scene: two boys shot execution-style while playing a video game.
One of the boys was using the bathroom at the time of the shooting, which saved his life.
Voight has a chat with Kareem, the leader of the Westside Hustlers, who informs him that his nephew was one of the boys killed.
While he gives Voight some time to find the killer, he informs him that there's a broken community who wants someone to pay for the murders.
Fighting against time, Intelligence dedicates all of their resources to finding the person capable of killing two innocent boys.
Interim Mayor Crawford tells Voight about a state-of-the-art software that's being developed to help with facial recognition.
It tells them with a 99.64 accuracy that the man they spotted near the crime scene just a few minutes after the murders is Marcus West.
Voight's uneasy about using the software's intel because he said it's like doing the case backward.
The machine gave them a suspect before they even had a case. But Halstead reminds him that there are two murdered kids out there and technology believes West is responsible.
What else are they waiting for? So, Voight agrees to bring him in. When they bust into Marcus' house he runs from the cops later telling Halstead that it's just a natural reaction for African Americans.
But he denies having any involvement with the murder and assures him that despite being a junkie, he's not a murderer.
Halstead realizes that they're running out of time so he books him into County to break him. But that plan backfires when someone stabs Marcus 7 times in lock up.
After the attack, Marcus is placed in a medically induced coma to keep down the brain swelling. Halstead eventually learns that he has died. With time slipping away from them, Voight urges his team to build a case and find the link connecting Marcus to the murders.
Intelligence goes through the log of inmates that could have been responsible and realizes Peter, one of Kareem's men, turned himself in on bogus charges that same night.
At the same time, Atwater tracks down Marcus' friend Ruben, who gives his friend an alibi, while Burgess and Upton talk to the surviving kid who informs them that he heard gunshots before a door was kicked.
This tells them that it was an inside job by one of the Hustlers.
As they narrow down the suspects, Voight puts his money on Prophet, Kareem's right-hand man, who has been trying to sway the investigation from the very beginning.
Voight meets with Kareem and Prophet to inform them that Marcus was innocent and that they believe someone from inside the Hustlers is involved thus triggering Prophet.
They watch as he takes the bait and attempts to dump the bag with all the weapons and money in a random car.
Voight confronts Crawford about his problematic software, which was revealed not to work well when it comes to dark-skinned African Americans, but Crawford tries to point the blame at Halstead. When Voight comes after him, he informs him that the optics aren't good for any of them.
Voight offers up a solution that isn't exactly "what they taught in the police academy."
Mayor Crawford addresses the public with information about the children's killer - Marcus West, who he says was detected using "state of the art" technology now making Chicago a safer place.
Meanwhile, Voight tells Kareem the truth about his friend Prophet and allows him to handle it however he sees fit.
Obviously, Kareem gets revenge by beating Prophet to death with the help of his boys. Voight watches as they dispose of the body.
When Halstead confronts Voight about what he did, Voight tells him to "let it go."