Murder at the Gallop (1963)
Miss Marple and Mr. Stringer are witnesses to the death by heart attack of elderly, rich Mr. Enderby. Yet they have their doubts about what happened. The police don't believe them, thus leading Miss Marple to yet again investigate by herself. based on novel or book, heart attack, horseback riding, amateur detective, testament, barn, covered investigation, eavesdropping, black and white, murder mystery
ETC.
