Three illustrious members of the Von Treylan Trust - the fellowship of which funds an orphanage - have been murdered in manners meant to suggest a suicide. When a bus carrying several of the orphans crashes and the driver inexplicably burns to death even though the bus did not catch fire, Colonel Bingham (Christopher Lee, HORROR EXPRESS) suspects that it was not an accident since the bus was also carrying three more of the board's trustees. Since the trustees have all left their entire fortunes to the fellowship, it increases with each death, but Bingham thinks the motive of a final benefactor is too blatant to explain the murders and asks pathologist Sir Mark Ashley (Peter Cushing, THE CREEPING FLESH) to help him find another connection between the murders of the trustees (which only have in common mutilating injuries to the face). Young orphan Mary (Gwyneth Strong, AFRAID OF THE DARK), who was uninjured in the crash but has been experiencing nightmares suggesting repressed memories of a traumatic fire (brought on by the driver's death) and Dr. Haynes (Keith Barron, AT THE EARTH'S CORE) is reluctant to let her be returned to the orphanage until she undergoes psychiatric treatment. Complicating matters is Anna Harb (Diana Dors, BERSERK), an ex-murderess claiming to be Mary's mother, who wants to take the girl with her and threatens Haynes and others. After Haynes and nosy reporter Joan Foster (Georgia Brown, TALES THAT WITNESS MADNESS) set up a disastrous reunion between Anna and Mary, and Haynes is found murdered, Mary is returned to the orphanage (on the Scottish island of Bala). Bingham and Ashley's plans to exhume the three dead trustees are put aside when they learn that Anna's car was discovered on the Bala ferry (the script would like us to think she's a suspect in the deaths of the trustees but we know she's a red herring). Bingham, Ashley, and Foster arrive on the island as the authorities search for Anna. They are also just in time to witness a yacht explosion which knocks off five more of the Van Treylan trustees. The search intensifies when a child from the orphanage disappears and is found ritually murdered. Bingham insists on increased security for the orphanage since Mary's birthday party - complete with Guy Fawkes bonfire - is planned for the evening. Meanwhile, Foster plays the tape of Mary's hypnosis session to Ashley, and they make a chilling discovery about the connection between the dead members of the Van Treylan Trust and orphanage.

In 1972, actor Christopher Lee and former Hammer producer Anthony Nelson Keys formed the production company Charlemagne to produce adaptations of four novels Lee had optioned, including John Blackburn's "Nothing But the Night" (the film ended up being the only production for the company). The screenplay and the resulting film are more than a little lopsided, with much of the middle devoted to Bingham arguing with the orphanage over security intercut with Anna trying to elude the search party in the forest, and most of the clues to the mystery are shoved into a pair of scenes late in the film (with Bingham reaching the same conclusion as Ashley and Foster simultaneously, but without their evidence). The climax anticipates a horror sub-genre that would not become truly in vogue until the mid-seventies, and the ending is somewhat shocking for a British picture (although seventies British horror was starting to lean towards more downbeat endings). The film also features Michael Gambon (TV's MAIGRET) as a Scottish inspector and Kathleen Byron (BLACK NARCISSUS) as the orphanage's doctor, but the interesting supporting cast (including Brown, Byron, Gambon, and Fulton Mackay as the Scottish police chief) are mostly underused, and seventies Hammer/Tyburn cinematographer Kenneth Talbot (THE DEVIL WITHIN HER) lacks visual flair. The understated score of Malcolm Williamson (BRIDES OF DRACULA) quotes English traditional song "Ten Green Bottles" (which has been adapted into our American driving song "99 Bottles of Beer").