Not appropriate for kids under 12 or so, I would say. Jr. High at the youngest.
my favorite amongst the Cormier novels.
Cormier is the master of surprise endings and this won't disappoint the reader. A young girl is attacked in her home and left in a coma. The attack is witnessed by a young man witnesses the whole thing. In love with the girl, he becomes "The Avenger" rather than her savior for GOOD REASON!