A schoolteacher (Fontaine) has a nervous breakdown after being exposed to witchcraft while teaching as a missionary in Africa. On her return to England, she is hired by a wealthy brother and sister (McCowan and Walsh) to become head teacher of their small private school in a rural village. There she becomes suspicious of the way the villagers are treating a 14-year-old girl (Boulting); her investigations point to witchcraft.
The town of Hambledon in Hampshire was the filming location for the fictional village of Heddaby. Interiors were filmed at Hammer's usual studio at Bray in the same year the famous horror film company vacated their home altogether for (mainly) Elstree and Pinewood.
The cast featured child-actor Martin Stephens, then 18, better-known for playing Miles in the 1961 British horror The Innocents. The supporting cast also included Hammer regular Duncan Lamont, as well as John Collin, Michele Dotrice, Leonard Rossiter and Bryan Marshall.
In a later magazine interview Nigel Kneale said he was dissatisfied with the way the film had turned out. Personally he found modern black magic practitioners to be fairly risible and he had intended to poke fun at the idea of an English coven. However his blackly comic touches were smoothed out by the production team, who wanted the film to be entirely serious.