The Adventure of the Blanched Soldier."
Many years have passed, and Sherlock Holmes is now living in the countryside with a housekeeper and his bees. He's settled into a life with beautiful scenery, a variety of neighbors, and no mystery or adventure. That is, until a teacher at the local prep school staggers up and collapses dying at his feet. Fitzroy McPherson appears to have been accosted while on an ocean swim, some unknown assailant leaving whip-like lashes crisscrossing his back. When McPherson dies of his injuries, Holmes must determine who might have been responsible for his death.
As far as the mystery in this short story goes, there's a decided lack of suspense and plausibility here. If a man lays dying after an ocean swim, it's hardly a difficult leap to suspect (SPOILER) that some sort of mishap involving marine life might be the cause. So much for the mystery. And for the dying man to gasp out "the lion's mane" as his dying words -- referencing a (FURTHER SPOILER) particular breed of jellyfish -- is awfully convenient for plot (though inconvenient for investigation). He might just as easily have said something obvious and instructive like "jellyfish." So much for plausibility.
But what is intriguing about the story, and what sets it quite apart from the other Holmes-narrated "Adventure of the Blanched Soldier," is its setting in both a time and place quite different from every other Holmes mystery. This retirement-in-the-countryside setting provided the most direct inspiration for the novel A Slight Trick of the Mind (and its film adaptation, Mr. Holmes), and it's easy to see why: it feels like there are other tales that could be told in this different mode. This story presents Holmes somewhat out of his element, with several new surrounding characters one might imagine to be recurring in subsequent tales. It's rather like a modern television series doing a major creative "reboot" going into a new season... though it turns out this series was actually near the end of its run.
The lacking mystery does drag this tale down from where I might have scored it, but the fascinating changes to the formula had it starting from a higher mark. I give "The Adventure of the Lion's Mane" a B-.