Prince Zaleski

Prince Zaleski, an exiled Russian nobleman, inhabits a half-ruined abbey in Wales, where he spends most of his time smoking cannabis and opium, reading from his library of medieval books, or admiring his collection of rare curios dating from ancient antiquity. His retirement from the world is occasionally interrupted by his friend Shiel, who comes to seek Zaleski's help in solving mysteries that have baffled the greatest minds in Britain:

In "The Race of Orven," Zaleski must unravel a case involving a burglary, a murder, a floating phantasm, and three severed fingers.
In "The Stone of the Edmundsbury Monks," the prince races against time to solve the mystery of a jewel from the Crusades that may cause a man's death.
And in the final story in the collection, "The S.S.," an inexplicable wave of thousands of apparent suicides puts Zaleski to the ultimate test and leads to a deeply disturbing conclusion.

[Source: https://www.risingshadow.net/book/26648-prince-zaleski]