- By Paul Halter
- First published: France: Le Masque, 1993
- Translated into English as The Demon of Dartmoor by John Pugmire, Locked Room International, 2012
Le Diable de Dartmoor is one of Paul Halter’s finest accomplishments in the orthodox genre.  The author himself only considers it a good average book – not his favourite, but representative. “A curse, an extremely simple crime trick; and Inspector Hurst grumpier than ever.” As such, it would make an ideal place for the reader new to Halter to start.
The scene is Devon, with its sleepy villages and rugged tors – familiar to detective readers as the setting of The Hound of the Baskervilles, if not The Sittaford Mystery. Halter had recently visited there – “My first pilgrimage to England since I started writing… I brought back quite a few books of legends. I was able to see the places that lend themselves perfectly to this kind of inspiration.”
The village of Stapleford seems to be haunted by an invisible fiend. Three girls are pushed to their deaths; shortly before their murders, they were seen laughing and talking to apparently empty air. A village drunk sees a headless horseman ride up into the sky. In Trevice Manor, decades before, another young woman fell downstairs. And now, in 193–, brilliant actor Nigel Manson is flung to his death from a window in the same house – yet nobody could have committed the crime. Is it mere coincidence he was starring in The Invisible Man?
Halter offers one of his neatest puzzles. We should tumble at once to the method, and then to the killer; it is “a murder of a stunning simplicity”. That stunning simplicity places the method in the same class as Chesterton‘s “Hammer of God” or Carr‘s Crooked Hinge or Death in Five Boxes. But the trick is so simple, so obvious, that we never consider it. “To have been stumped by such child’s play is enough to make me blush with shame,” Dr. Twist remarks. “In all my career, I’ve never come across such a mysterious puzzle with such an incredibly simple solution.” On top of that, Halter offers a culprit whose identity is a genuine surprise. Both method and identity are finely clued; certain physical evidence (ROT13: gur pnzren fznfurq vagb n gubhfnaq cvrprf) and odd behaviour (n eryhpgnapr gb ivfvg Qriba) point straight to the murderer. French critics of the time were impressed; Soupart, Fooz and Bourgeois hailed Halter as the ideal amalgam of Carr and Pierre Véry.
 La 7è hypothèse, however, is arguably Halter’s best: a tour de force of plotting, as audacious as Sleuth or Death Trap.