Plot hole: At the end of the film the boss says that he and Miss Fitzgerald are going to go on holiday together to Paris (talking about the actual city, not the secret code they have invented). However, the film is set in 1940 and Paris would have been an unusual place to take a holiday at this time, considering France was in the middle of a war... Pretty dangerous for civilians even though America was still neutral at the time.
Plot hole: When Margaret has to collect the $50,000, she goes around to various banks trying to get a loan on their house, which she can't get because her husband, co-owner of the house, isn't around. Why couldn't she just have taken the papers, said she was going to take them home to her husband, forged his signature, and brought them back? You can't exactly say she has either moral problems or isn't devious enough, since we've already seen her stuff a body into a dinghy, toss it into the lake, and come back to her house looking fairly normal.
Factual error: The movie "Cat's Meow," about a real incident that occurred on William R. Hearst's yacht, includes a scene where a female guest, awakened by a gunshot, is wearing hair clips. Those objects were not available in the 1920s, and even if they were, they are totally ineffectual on her combed-flat hair style.
Revealing mistake: When Paul is in the car trying to escape, he hits one of the villagers. The man is obviously yanked back by a harness before the car hits him.
Continuity mistake: During the opening scene at the Istanbul night club, Tasha de Vasconcelos' hair goes down for a lengthier portion in front of her shoulders compared to the close-ups when they barely come off the left. (00:01:10)
Factual error: When the protagonists arrive to Patmos, latitude and longitude are switched the other way around at 26°489 and 37°411. Moreover, that's not Patmos, but Anydro Patmou, an uninhabited islet unlike what is shown here.