The Horrid Mysteries, subtitled "A Story From the German Of The Marquis Of Grosse" is a translation by Peter Will of the German Gothic novel Der Genius by Carl Grosse. It was listed as one of the seven "horrid novels" by Jane Austen in her Northanger Abbey and also mentioned by Thomas Love Peacock in Nightmare Abbey. It was first published by the sensationalist Minerva Press in 1796.
The hero of the tale, the Marquis of Grosse, finds himself embroiled in a secret revolutionary society which advocates murder and mayhem in pursuit of an early form of communism. He creates a rival society to combat them and finds himself hopelessly trapped between the two antagonistic forces. The book has been both praised and lambasted for its lurid portrayal of sex, violence and barbarism.