The Mirror Crack'd (1980)

Based on the novel by Agatha Christie. The year is 1953. The small English village of St. Mary Mead, home to Miss Jane Marple, is delighted when a big American movie company arrives to make a movie telling of the relationship between Jane Grey and Elisabeth I, starring the famous actresses Marina Rudd and Lola Brewster. Marina arrives with her husband, Jason, and when she discovers that Lola is going to be in the movie with her she hits the roof as Lola and Marina loathe each other on sight. Marina has been getting death threats and at a party at the manor house, Heather Babcock, after boring Marina with a long story, drinks a cocktail made for Marina and dies from poisoning. Everybody believes that Marina is the target but the police officer investigating the case, Inspector Craddock isn't sure so he asks Miss Marple, his aunt, to investigate...