The RAF was established in April of 1918 with their own unique rank structure. The first murder victim is called "Captain" Hamilton, another character is "Major" Jenner, and a third is listed as "Flight Commander". NONE of these are RAF ranks. The ranks (low to high) are actually "Pilot Officer", "Flying Officer", "Flight Lieutenant", "Squadron Leader", "Wing Commander", "Group Captain", "Air Commodore", "Air Vice Marshal", and "Air Marshall". To be a "Captain" or "Major" they would have had to be in the Royal Flying Corps which was a part of the British Army and was disbanded during World War One. "Flight Commander" was never an Army or RAF rank.
The character of Paul Gray, accused of the murder, is clearly identified by newspaper headlines as well as in the dialogue, but is billed at the end of the film as 'Hugh Gray'.
This Hollywood film makes the common mistake of including the sound of chirping crickets at night in England. Crickets are not heard in England.
Despite the title, all but the first few minutes of the movie takes place in a house in the country.