The Adventure of the Circular Room

Just read The Adventure of the Circular Room in The Game Is Afoot collection my husband gave me. It’s an August Derleth story that he apparently first wrote as a Sherlock Holmes pastiche and again as a Solar Pons story, but I swear I’ve read (or heard or watched) it elsewhere as a story with another detective. I could swear it was Christie’s Poirot, but I guess it could just as easily be the dim memory of an Adrian Monk or Banacek episode.

If you have some idea where I might have encountered the story—maybe a radio adaptation?—I’d appreciate your telling me. It’s driving me crazy.