Long Way Down by Jason Reynolds

After Will’s brother is shot in a gang crime, he knows the next steps. Don’t cry. Don’t snitch. Get revenge. So he gets in the lift with Shawn’s gun, determined to follow The Rules. Only when the lift door opens, Buck walks in, Will’s friend who died years ago. And Dani, who was shot years before that. As more people from his past arrive, Will has to ask himself if he really knows what he’s doing.