White, Ethel Lina: They See in Darkness (1944): V1
 

Ethel Lina White (1876-1944) took up writing books in the late 1920s, first trying mainstream novels, and then turning to slightly gothic thrillers from 1931.

Oldtown is a picturesque, historic place, with a square of characterful houses nestling at its centre, and is home to retired colonial masters and friendly locals. A wealthy, reclusive sisterhood lives there too, in a large mansion, Cloisters; a group known locally as the 'Black Nuns', who are said to have extraordinary healing powers.

But a killer is at work in Oldtown

Original book covers are not easy to come by and may still be copyright in some cases. I have made up a generic cover employing a vignette from a photograph of Ms White taken in the 1920s, and the rest is typography.