Murder once again touches the residents of St. Mary Mead, home of Miss Jane Marple. American actress Marina Gregg and her husband have recently moved into the area, and host a garden party as a fundraiser for a local charity. One of the guests, Heather Babcock, dies after drinking a poisoned cocktail. Because Marina Gregg had shared her drink with Mrs. Babcock, it is assumed that Gregg was the intended victim. Miss Marple joins forces with Chief Inspector Craddock to sort out the confusion and identify the murderer.