I haven't read this book, but this is what the back cover says:

No one could understand why Colin and Roy were best friends. Colin was so shy; Roy was so popular. Colin was nervous around girls; Roy was a ladies' man. Colin was fascinated by Roy--and Roy was fascinated by death. Then one day Roy asked his timid friend, "You ever kill anything?" And from that moment on, the two were bound together in a game too terrifying to imagine... and too irresistable to stop.