Harlan Coben’s The Five
When they were twelve years old, Mark, Pru, Danny and Slade were out together in the woods. Mark’s five year old brother Jesse was bothering them. They told him to get lost. Jesse ran away. He was gone. Never seen again. Twenty years later, Danny - now a detective - learns some shocking news. Jesse’s DNA has been found at a murder scene. He is alive and out there. Somewhere.