Murder at the Gallop (1963)

While out collecting for charity, Miss Jane Marple (Margaret Rutherford) visits an antisocial villager (Robert Morley), and he suddenly drops dead in her presence. Suspicious of the circumstances, Marple eavesdrops on the reading of his will and subsequently shadows various members of the family who seem suspicious. As the bodies pile up, Miss Marple suspects she has the guilty party cornered, but she needs to find the last bit of proof before it's too late.