The Strange Affair of Uncle Harry

The Strange Affair of Uncle Harry is a 1945 film noir directed by Robert Siodmak, starring George Sanders as an aging bachelor who looks after his two sisters, one of whom tries to sabotage his romance with his coworker. It is based on the play Uncle Harry by Thomas Job.

Everything is disrupted by the arrival of a new young female designer at the mill. Deborah Raines comes from New York and is slim, elegant, and very welldressed. She clearly likes Harry and they fall in love. Planning to get married they aim to both live in the big family house, but this involves the sisters finding a new home. Whilst this is not an issue for Hester, Lettie is very resistant. After several months of having their marriage plans sabotaged, one Sunday, Harry and Deborah plan to run off to New York and just get married that evening. However their plan is thwarted when Lettie collapses and is taken to hospital. Deborah makes Harry choose Lettie or her. He chooses his sister and they part, seemingly forever.To make things worse, Harry hears that Deborah is getting married in New York. Harry feels betrayed and recalls that Lettie bought some poison for the possible euthanization of their dog. ........

Source: Wikipedia