The “sleeper” of folk horror’s “Unholy Trinity,” this Tigon shocker helped build the foundation of the folk horror trope of the terrors that lie beneath the soil. When a nonhuman skull is unearthed in seventeenth-century rural England, it spawns a frenzy of carnal insanity—embodied in an infamous performance by Linda Hayden (House on Straw Hill) as a succulent teen temptress who leads a satanically fueled youth revolt. The English countryside is beautifully and threateningly rendered by director Piers Haggard (who would return to folk horror with the last installment of the Quatermass series in 1979), whose depiction of pagan depravity is punctuated by an iconic and deeply unnerving score by composer Marc Wilkinson.