Ethel Lina White 
They See in Darkness [EPUB ebook] 

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, and a series of murders has thrown the inhabitants into blind, unreasoning terror, a fear of darkness and of strange sounds — sounds such as the pitiless beat of following footsteps. Suddenly the town is plunged into a miasma of fear and superstition …