A man has a gun in his backpack as he nervously waits for a bus. Someone says something to him and he jumps. The other person just wants to thank him for his service. The bus comes and they both get on it.
The man, Ernest Williams, turns out to be going to the police station to turn in the gun. He wants to be able to buy a clarinet for his young nephew. But the gun has blood splatters on it and Williams is arrested. At the station, he tells Dawson and Laura that he found the gun under Andre's mattress. When Andre gets home from school, he plans to confront him about it.
Dawson and Laura talk with Andre, who denies knowing anything about a gun or a shooting.
Meanwhile, Stone and Valdez go up against a new attorney, Bogart, in the trial of a gang member, Chris Stackhouse, accused of killing a ten-year-old girl during a gang war. The trial is interrupted by Dawson and Laura, who have news: the gun in Andre's room is the gun used to kill the little girl.
Jeffries is unhappy that they can't get a murder conviction with all the violence going on, but Stone thinks they have the wrong guy. During a continuance hearing, Bogart gets Stackhouse released without bail pending his new trial in one week's time. Dawson and Laura take Stackhouse home, where he is shot by another gang member who thinks he snitched to the cops.
Stone finds out that the gang is using social media to plan violence against rival gang members. He wants to shut down all of the suspected gang members' smartphones. Meanwhile, Williams tells the investigators that Andre's cousin Keo was here the other night in dirty clothes and gave Andre a brown bag with something heavy in it.
Stone, Dawson and Atwater try to question Keo, who is uncooperative.
Jeffries doesn't like Stone targeting cell phones because this policy will affect many kids of color. He lets Stone do it but says that he hopes nobody dies from not being able to use their cell phone in an emergency.
A judge grants a hearing on this matter for next Friday and wants the ACLU there. Stone insists on a hearing right away.
During the hearing, the phone company argues that as a public utility they can't pick and choose who to provide service to and that only they can decide someone violated the terms of their contract. An ACLU rep argues free speech includes the right to plan gang activities on a cell phone.
The judge says she is sure she will be struck down on appeal, but grants the injunction against the suspected gang members having phones as a matter of public safety.
Valdez wants Williams and his nephew to testify but Williams refuses to because it's too dangerous. Andre is terrified because Keo threatened him at school. Valdez thinks arresting Keo will solve that problem. Williams says it won't and leaves with Andre. They are going to go into hiding to try to stay alive.
Jeffries tells Stone about a lawyer who made paintings of every tree used to lynch a black man in Tennessee. He tells Stone the issues facing people of color in Chicago are far more complicated than they seem. But he is sure Stone will find a way to get Keo arrested.
Stone and Valdez decide to use Stackhouse as bait. Bogart is unhappy with this unethical behavior but Valdez talks her into it.
Keo is arrested as a material witness and taken to court. He blames his mom not paying the bill for his phone not working.
On the stand, Keo is questioned about his whereabouts and his giving Andre the gun, but he denies both. However, he gives himself away when he checks the gun and knows the magazine jams.
Keo tries to run away and is arrested by the bailiffs.
The gang celebrates their win, but then they get a call. Andre is found dead.