In earlier comment I speculated on the difference between the ending of the film itself and the novel on which it is based, "Before the Fact", by Francis Iles. According to the eminent film historian David Shipman, the book was about a woman who gradually realises that her husband plans to murder her, but who is so much in love she does not mind. He quotes Hitchcock as saying the inappropriate ending of the film came about because the producers, R.K.O., would have refused to let Cary Grant be a murderer. See David Shipman, "The Story of Cinema" (1984) at p.582.
