Gladys and Annie Barnes are impoverished sisters who have seen better times. They live in a modest cottage in the backstreets of Highate with Mr Fisher, a mild but eccentric old man living secretively in the attic above them. Their quiet lives are thrown into confusion when a new landlord takes over, a dreaded and unscrupulous 'rackman'. He installs his wife in part of the cottages in the hope that there she will recover from an unspecified malady. With a mounting sense of fear, Gladys and Annie become convinced she is possessed by an evil spirit...