Following up on "His Last Bow" (which in fact wasn't the "last bow" of Sherlock Holmes), "The Adventure of the Mazarin Stone" is the only other Sherlock Holmes adventure written from a third-person perspective. Holmes has been tasked with locating a crown diamond, and has zeroed in on the criminal responsible for stealing it. Unable to deduce exactly where it has been hidden, Holmes invites the culprit himself to Baker Street, for a dangerous meeting in which he intends to coax out the information to complete the case.
There's a lot that's curious about the structure of this story. It's one of only two stories in the canon written in the third person; indeed, Watson (who usually recounts these adventures) has little more than a cameo in the tale. It turns out that the reason for this is that "The Mazarin Stone" was in fact not originally conceived of as a short story. Instead, this is an adaptation of a stage play called "The Crown Diamond."
This origin explains more that's odd about the tale. It takes place entirely in the lodging at Baker Street -- in other words, on a single theatrical set. There's an elaborate ruse involving "off-stage sound effects" and a secret passage. That Holmes would have built such a passage in his house is bizarre to contemplate, but it certainly would have made for a tricky finale to a night at the theater. (The reveal feels almost like a magician performing a trick.) Indeed, much of Holmes' behavior in this tale seems even more dramatic than usual -- though very much in the spirit of a staged melodrama.