[The Mysteries of Udolpho] is a kind of mystery-machine, of course, full of local puzzles and conundrums.
»Terry Castle, in her introduction to Ann Radcliffe’s The Mysteries of Udolpho. Oxford World’s Classics. Oxford, 1998.
Given that the solution to one of the novel’s puzzles is straight out of an episode of Scooby Doo, “mystery-machine” is an apt choice of phrase.