I read this a long time ago, and although I remember the premise, I don’t remember what the final solution was. I’d like to read it again if I can find it.
Lord Whatsit was found shot through the chest with a large caliber bullet (bullet so severely damaged they couldn’t tell what kind of gun fired it). He was in a sort of turret room, sitting in a chair and facing the one open narrow window slit (like the old archer slits in castles) and there were a couple of other windows that were rusted closed. There was one door, locked on the inside, and also manually bolted on the inside, separate from the lock. No gun was found in the room.
The authorities left nothing undone to try to find another way in or out of that room. Wainscoting removed, windows minutely examined, outside of tower examined (nothing climbed up from the ground or down from the roof). The shot was (possibly) heard by a witness a small distance away, and possibly a small splash heard right afterwards in the ocean immediately below. No ships or planes or other air vehicles (e.g. balloons) were in the vicinity at the time.
Ring a bell? It’s driving me nuts. I’ve checked John Dickson Carr’s oeuvre and it doesn’t seem to be one of his. As I remember, it’s a longish short story.
There’s a Sherlock Holmes story that involves a suicide using a gun tied to a weight by a string. The weight was suspended just over the railing of a bridge, and the gun disappeared into the water under the bridge after the fatal shot was fired. So the suicide looked like a murder. Could that be what you are thinking of? If not, I suspect the splash in the story in your memory involved a similar gun-string-weight ruse.
The story I was thinking of was The Problem of Thor Bridge. Not a locked room mystery, but a method of weapon disposal that might relate to your locked room and splash.
I don’t know of anything exactly as you describe, but the second Sherlock Holmes story , the novel The Sign of Four describes a man killed with a poisoned dart in a locked room with no apparent ways in or out.
Closer, perhaps, is the Robert H. van Gulik Judge Dee novel The Chinese Maze Mysteries, in which a scholar is killed in his locked library by a poisoned dagger, with no ingress or egress or open windows. A pretty clever one, that. Based on a reportedly real Chinese account, although it wasn’t a locked-room mystery in real life
Not quite what you were looking for, but there was a Father Brown story in which an American millionaire was found dead with an arrow in his chest in the topmost room of a tower with an open window but no corresponding site from where an arrow could be launched. The door was locked but there was no splash as in your description.
There’s a Carr story that tracks a family legend in which a person who defies the family has their eyes gouged out by ghostly crows in a locked tower room. Could that be it?
Apologies for any vagueness; when I said it sounded like THE BRADMOOR MURDER, it was because there was a splash, and because there wasn’t a ghostly crow or a poisoned dart or a dagger or an arrow or whatever, in that one; just a large bullet in the titled corpse near that slit in the wall for a back-in-the-day archer to fire out of.
I have checked out all the suggestions, and this is it. For some reason I remembered the splash because the very old ear-witness who heard the shot and the splash thought it was the sound a devil’s imp would make if it fell into the water, and she was convinced it was the work of the devil.
So thanks, The Other Waldo Pepper, now I can read this through again.
I know the story turned out to be The Bradmoor Murder but I couldn’t resist the Carr reference. John Dickson Carr was the absolute master of the locked-room mystery. I do urge all lovers of this genre to read The Three Coffins (also known as The Hollow Man). It was voted by 17 well-known mystery writers as the best locked-room mystery ever written and it fully deserves that accolade, it really is the cleverest and most elaborate fictional murder ever committed. When I first read it and discovered the solution I instantly re-read it just to admire the murderer’s work all over again.