Elwyn and Lloyd Clayton are twin brothers (played by George Zucco). Elwyn worships Satan and is a magician. Because of this, Lloyd secretly kills his twin. Being killed of course greatly angers Elwyn, who comes back from the dead as a vampire to exact his revenge.
This is a good film, and you gotta love George Zucco (Well, you don’t have to, but it’d be weird if you didn’t)