Ghost Medicine by Andrew Smith

There is a seventeen year old boy name Troy who lives on a range with his dad and horse. He spends a lot of time with his friends Gabe, Tom, and his girlfriend Luz. One day a kid name chase does something to Luz, gets shot/ injured by Gabe and they all go to the cabin Troy found to hide. Once they see chase following they hide in the woods. Something happens in the woods that brings them closer than they ever have.