George Kingsley was run over while crossing the street by a speeding gangster. Before his imminent death his best friend and mad scientist, Dr. Ernest Sovac thought he would be a good friend and replace the damaged parts of George’s brain with that of the gangster that ran him over.
Eventually, something terrible happens. George randomly begins acting like the gangster that nearly killed him. Slowly at first and then permanently. When the gangster’s willpower overcomes George’s we find out that there was a half a million dollars in 1940’s money lying around somewhere.