Wrong place wrong time

Then you spot him : he's with someone. And - you can't believe what you see - your funny, happy teenage boy stabs this stranger. You don't know who. You don't know why. You only know your son is charged with murder. His future is lost. That night you fall asleep in despair. But when you wake... it is yesterday. The day before the murder. Somewhere in the past lie the answers - a reason for this crime.
And your only chance to stop it...