This is the start of a short 3 episode adventure in the new Regency Cthulhu setting by Chaosium. It is an adventure called The Long Corridor, where Lovecraft and Jane Austen collide at a fashionable ball.
The library at Cassiobury in the 1830s. Etching from “The History and Description of Cassiobury Park, Hertfordshire, the Seat of the Earl of Essex” via the Metropolitan Museum of Art