Murder with Mirrors (1985)

Christian Gilbranson (John Woodvine), Miss Jane Marple's (Helen Hayes') lawyer, persuades her to visit the baronial estate of his stepmother, Carrie Louise Serrocold (Bette Davis), an old friend of Marple's. Carrie Louise's devoted husband Lewis (Sir John Mills) has turned the manor house into a halfway house for young men with criminal records, and has hopes of expanding the facilities. He confides to Miss Jane Marple that he suspects that someone is slowly poisoning Carrie Louise with arsenic. One of the young charges, Edgar Lawson (Tim Roth), claims to be Lewis' illegitimate child and wants his alleged father to acknowledge him. While they are arguing behind closed doors, a gun is discharged, and the visiting Gilbranson is found murdered in another room. It is up to Miss Jane Marple to aid crusty Inspector Curry (Leo McKern) discover the murderer's and poisoner's identities.