In the tradition of the old "Ace Doubles" (flip one book over to read the second title), here is the tenth Wildside Double:

VALDEMAR'S DAUGHTER: A ROMANCE OF MESMERISM, by Brian Stableford

Following the sad demise of Ernest Valdemar, as related in the story by Edgar Allan Poe, his mortal remains are sent to his daughter in Paris--but go astray--and detective Auguste Dupin must track them down. The Comte de Saint-Germain seems implicated in the mystery. Meanwhile, the great writer Balzac lies at death's door, convinced that only Valdemar's body can save him. Will Dupin thwart his adversary in the nick of time?

THE MAD TRIST: A ROMANCE OF BIBLIOMANIA, by Brian Stableford

The Comte de Saint-Germain has come into possession of The Mad Trist, the book from which Edgar Allan Poe and Roderick Usher read aloud before the collapse recorded in "The Fall of the House of Usher." He intends it as a gift to detective Auguste Dupin, but Dupin's friend, Richard Carstairs, cannot deliver the volume immediately. Richard is unintimidated by the prospect of reading a supposedly cursed book--after all, Dupin has a whole shelf full of them A classic tale of horror.