At an end-of-London-season soirée, the young Hungarian scholar-dilettante Janos Bátky 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 — Bátky receives a mysterious phone call warning him not to go; but he does and finds himself in 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.