Cause for Alarm! (1951)

Invalid George Jones (Barry Sullivan) is both physically and mentally ill. He mistakenly believes his wife Ellen (Loretta Young) and his doctor (Bruce Cowling) are having an affair and also planning to kill him. He writes a letter to the district attorney detailing their alleged murder plot. After he has Ellen give the letter to their postman, he reveals its contents to her and then threatens her with a gun. The excitement proves to much and George suffers a fatal collapse. Now Ellen must find a way to retrieve the incriminating letter.