Not a very compelling film at all, I erroneously believed it was from the late thirties, perhaps an English suspense drama. Upon looking it up, I see it is from 1956! Inexcusably dull film.
Derek Bond as the husband agrees with his French mistress Nicole Maurey that he will kill his invalid wife so they can be together. He devises 'an ingenious plot' by making sure he is seen voyaging out in a yacht, racing back in a rented speedboat or something, murdering her, then hurrying back, establishing his alibi. Apparently automatic pilot was still a bit of a novelty as that seemed to be the evidence that turned the tide. French witnesses to an unidentified speedboat and a gas fume leak in the yacht were also little tidbits to pay attention to. Pity Hitchcock couldn't have gotten hold of this one.
Bond sought to off the Inspector with that gas fume leak on the yacht when he lit a match but the Inspector was out of matches. Suddenly Maurey was shocked by the man she saw. Why, when she had pushed him into murdering his wife? Maurey and Bond are for some reason listed as the stars but the investigating detectives were more compelling to watch.
Look for 'Double Indemnity' instead.