We are in London, where fog has blanketed the city for days. You can't even see your hand in front of your face, much less someone else's hands around your neck! Yes, someone is strangling the great men of London, and Lord Montague (Young), aka Monty, has narrowly escaped becoming the newest victim. He slips into Scotland Yard and has a nice leisurely chat with the inspectors about what has happened. He also downs several brandy and sodas, leading him to make this observation:
"Being dead must be like living in America -- it's a dry state."
Get it? Prohibition?
I know you're out there, I can hear you breathing.
And sure enough, by the power of Roland Young's sideburns, they gather!
Also in the house are Lord John's sister, the seance-loving Lady Violet (Natalie Moorehead) and her fiancee, a physician (Ernest Torrence). And then we are visiting by Lady Efra (Dorothy Sebastian), whose late father was also a member of the regiment, and her suspicious guardian, Abdoul (Boris Karloff). More murders then take place, and the murderer is somewhere in the house!
Uncovering the bad guy requires a fake seance and a few other dramatic revelations that the actors react to as follows:
The story for "The Unholy Night" is credited to Ben Hecht. Considering that he did much better work later, we'll give him the benefit of the doubt and assume that his three other co-writers stripped all of Hecht's wit and cleverness out of this script.
Here are the complete credits for "The Unholy Night."