When a jewel robbery goes horribly wrong and their leader, Jack (Paul Naschy) is shot in the head, a group of criminals go to extreme measures to save their friend's life...With the help of a local doctor the gang devises a uniquely gruesome plan-to kill their worst enemy, throw his body in front of an oncomming train, and use the brain from the severed head as a transplant!  The operation is a success and all seems well...that is until the brain's former owner starts living out his murderous past through Jack, turning him into a mad-man bent on death and destruction!