Baron Zorn keeps his teenaged children locked up and drugged, fearing that his insane wife passed along a congenital curse to them before her own suicidal death. Elizabeth escapes for a brief tryst with a local before being recaptured and subjected to a bleeding process to ‘draw out the bad blood.’ Emil keeps trying to escape, but is thwarted time and again by his aunt Hilda who runs the house like a prison. One reason the siblings have to be kept apart, is their incestuous attraction to each other. Local wenches are being murdered in the woods, and the superstitious peasants think demons are responsible. A wandering Priest dedicates himself to root out the evil, but isn’t taken seriously. Arriving at the castle are two more interested parties: Mountebank scientist-huckster Falkenberg stands to make a small fortune if his strange apparatus can cure the children of their inherited evil. Young Carl simply wants to rescue Elizabeth… —IMDb
Peter Sykes is an Australian movie director born in Melbourne in the year 1939. He came to some prominance in independent British film circles for writing and directing the 1968 music/drama The Committee. He then went on to direct two episodes of the quirky adventure series The Avengers. Sykes’ first work in the horror genre was directing the 1971 film The Legend of Spider Forest. He immediately followed this up in 1972 with Demons of the Mind for Hammer Film Productions. Also for Hammer, Peter Sykes adapted Dennis Wheatley’s To the Devil a Daughter in 1976. Sykes also had an uncredited cameo appearance in the film as a man at an airport. In 1977 he directed the comedy/horror movie The House in Nightmare Park. —headhuntershorrorhouse.wikia.com
I love early 70's Hammer Horror because they became so sexually bold but this is probably the most boring movie you could imagine about incest, murder, and sanitariums. Actress Gillian Hills is beyond lovely; unfortunately, she's given absolutely nothing to do. The ending of the film admittedly packs a wallop but you have to endure a lot of over-acting, under-acting, and scene padding to get there.