Then about ten years ago a friend of mine recommended Rohmer's mystery novel BAT WING and even sent me a copy of it. It features another series character, Paul Harley, a former "diplomatic troubleshooter" for the British government who has retired from that to become a private detective. BAT WING is a British country house mystery, with Harley solving a murder that involves a lot of suspects, but there's a voodoo element to the plot, too, and the book is pretty creepy in places, as I recall. I enjoyed it a lot.
Fire-Tongue doesn't mean anything to Harley, but he knows that Nicol Brinn is an eccentric American millionaire who lives in London and has the hobby of risking his life in far-off places. Convinced that Sir Charles's mysterious death is really murder, Harley dives into the case, of course, which sets off a round of disguises, escapes, and chases. Harley winds up in considerable danger before he unravels the secret of the mysterious criminal mastermind behind the enigmatic name Fire-Tongue.
This novel is more of a thriller than an actual mystery. Modern readers might find the pace a little slow and the writing old-fashioned, but if you can put yourself in the frame of mind of a reader in the 1920s you'll probably find FIRE-TONGUE highly entertaining. I certainly did. The Stark House volume reprinting BAT WING and FIRE-TONGUE also includes an excellent introduction by Gene Christie. I suspect I'll be reading more by Sax Rohmer, if I can find the time.