Black Friday (1940) Boris Karloff

Boris Karloff stars in this sci-fi horror from 1940. When mild-mannered professor George Kingsley (Stanley Ridges) is fatally wounded, his friend Dr. Ernest Sovac (Karloff) performs illegal brain surgery to save him. After the operation, Kingsley is left with part of deceased mobster Red Cannon (Ridges)'s brain and as a result suffers from a split personality. He tells Sovac about a secret stash of money that Cannon stole. To locate the cash, Sovac hypnotises Kingsley so that Cannon's personality will take over, but this only makes matters worse for the professor. Bela Lugosi also stars as a gangster who is out to get the money for himself.