Miss Marple: A Pocketful of Rye (1985)

Wealthy business man Rex Fortescue collapses when he reaches his office. It is determined that he was poisoned. No one seems too upset, as everyone agrees that Rex was a tyrant. Soon however Rex's young wife also turns up poisoned. The maid, Gladyes, whom Miss Marple trained, writes to Miss Marple asking for help. Miss Marple arrives too late, as Gladyses' body is found strangled and strung up on the clothes line. Now it's personal, and Miss Marple is determined to see the murderer punished.