The Pendragon Legend — Antal Szerb

While visiting a Welsh castle, a young scholar finds himself at the center of occult rituals and a murder mystery in this “absolute treat” of a gothic detective story (The Guardian)

At an end-of-the London season soiree, the young Hungarian scholar-dilettante Janos Batky is introduced to the Earl of Gwynedd, a reclusive eccentric who is the subject of strange rumors. Invited to the family seat, Pendragon Castle in North Wales, Batky receives a mysterious phone-call warning him not to go. But go he does, plunging him into a bizarre world of mysticism and romance, animal experimentation, and planned murder. His quest to solve the central mystery takes him down strange byways-old libraries and warehouse cellars, Welsh mountains and underground tombs.
 
The Pendragon Legend is Antal Szerb's first novel and is a gently satirical blend of gothic and romantic genres, crossed with the murder mystery format to produce a fast-moving and often hilarious romp. But beneath the surface, the reader becomes aware of a steely intelligence probing moral, psychological, and religious questions.