This movie is sort of an inversion of the Hands of Orloff, in that a famous pianist dies and his hand comes back from beyond the grave to murder people...or does it?
In Italy, the pianist in question is living out the end of his life in a villa with his assistant (Peter Lorre), his nurse, some staff and the occasional visit from the chief of police or a musician/con man who sells fake antiques to tourists. The pianist has only one good hand and uses it to play special music arranged by the con man. The one-handed gent is also quite wealthy and decides to leave all his estate to his nurse. This angers Peter Lorre and the man's remote relations, who arrive to sue for the estate once the old man eats it after falling down some stairs. Once a crooked lawyer is killed off and the piano begins playing by itself, the characters gather to find the murderer.
All signs point to the one good hand somehow removing itself from the corpse and escaping the crypt in order to play piano and gain revenge. Lorre gets obsessed with the hand and seemingly does battle with it throughout the library. You'll have to watch to see what else happens but, needless to say, don't trust everything you see. This is a better little flick than I expected.