This Is The House

by Shelley Smith

[wyvernfriend]

Originally published in 1945 this does show some racism towards the "natives" and shows them being quite cliched, but it also does this for some of the British.  
 
Set on the probably fictional Apostle Island on the Windward Isles where the capital, Wigtown, is dominated by Premier Justice Antoine Jacques a Frenchman married to Julia who has been stricken with paralysis for many years, who is British, referred to as La Morte by many on the island. In the household is also her son, Raoul, her cat-lady sister, Hattie Brown and Prudence Whitaker, Hattie's secretary. 
 
Quentin Seal is a mystery writer, or at least he's using his writing to fund travel around the world. He writes when he has to but otherwise leads a life of idleness and travel.  He's on the island and visits the the Jacques house and accidentally becomes the discoverer of Julia's sudden death.  A tragic death but considered by some a merciful release.  Things are complicated more by questions of who was where when it happened.
 
Then the son is found stabbed to death and Quentin is called in to help the investigation and while he demurs at first he throws himself at the problem with all his ability.  It's full of twists and turns and complications and red herrings galore.  There's also an interesting twist to the end and the motives of some of the characters.
 
This could be: murder most foul, locked room (to an extent, in particular all the suspects have alibis); terrifying women, Amateur sleuth, cosy mystery, and Terror in a small town.  I'm going with Terror in a small town.