Egyptologist and professor Henry Morlant (Karloff) thinks an ancient jewel will give him powers of rejuvenation if it is offered up to the god Anubis. But when Morlant dies, his assistant Laing (Thesiger) steals the jewel. While a gaggle of interlopers, including a disreputable lawyer (Hardwicke) and a fake vicar (Richardson), descend on the professor's manor to steal the jewel for themselves, Morlant returns from the dead to punish everyone who has betrayed him.
Tropes used in The Ghoul include:
- Amoral Attorney: Morlant's lawyer Broughton is one of the people trying to break into his tomb to steal the jewel.
- Antagonist Title: The title refers to Professor Morlant after he has risen from the grave to avenge himself upon his tomb robbers. The actual protagonists are his heirs: Ralph Morlant and Betty Harland.
- Bad Habits: Nigel Hartley is a thief disguised as a country parson as part of his plan to steal the jewel.
- Black Dude Dies First: The first person killed by Morlant when he returns from the grave is Aga Ben Dragore's Arab servant Mahmoud.
- Buried Alive: If you believe the doctor, Morlant was never actually dead, but merely in a cataleptic trance, and thus was entombed alive.
- The Cavalry: A standoff between Kaney and Broughton and Dragore is ended by the arrival of the police who take the men into custody.
- Crusty Caretaker: Professor Morlant's manservant Laing shuffles around the Old, Dark House with a clubfoot, carrying out his master's spooky instructions for his internment while all the time muttering about what a dark business it is in a thick Scottish accent.
- A Foggy Day in London Town: Laing travels to London and attacks Betty on the street on a foggy night so he can steal her bag and plant a note in it.
- God Guise: Hartley places his arm through a fake sleeve to briefly pose as the god Anubis and take possession of the jewel.
- Grave Robbing: Multiple thieves are planning to break into Professor Morlant's tomb to steal the jewel he believes is going to resurrect him.
- Kissing Cousins: The romantic leads, Betty Harlon and Ralph Morlant, are distant cousins.
- Locked in a Freezer: After stealing the jewel, Dragore locks Betty, Ralph and Hartley inside Morlant's tomb, where they will suffocate if they are not found. The situation gets worse when a fire breaks out.
- Maybe Magic, Maybe Mundane: Rational explanations are presented for all of the events of the film. It is up to the viewer to decide which version they believe.
- Mineral MacGuffin: The item everyone is after is the Jewel of Light; either for its monetary value, or its supposed supernatural powers.
- Old, Dark House: Professor Morlant lives in a rambling old mansion on the Yorkshire Moors, lit entirely by candles.
- Our Ghouls Are Creepier: Professor Morlant is either a man raised from the dead by ancient Egyptian magic to avenge himself against tomb robbers, or a man in a cataleptic trance who was mistakenly entombed alive and who, upon awakening, went insane and believed himself to be a ghoul. Take your pick.
- Silly Will: Professor Morlant makes some very strange stipulations in his will, mostly connected with his burial, all of which relate to his belief that he is going to be resurrected by an ancient Egyptian jewel.
- The Vicar: Nigel Hartley presents himself as a bicycle riding country parson, who accuses Morlant of paganism and fears for the fate of his soul. However, it actually turns out to be a case of Bad Habits.