Longtime Hammer screenwriter Sangster’s final turn in the director’s chair for the studio sees him co-scripting a giallo-esque thriller with his usual emphasis on trust-issues. Judy Geeson is recovering from her nervous breakdown—or, maybe not; she’s convinced she’s being stalked, to the dismay of her school teacher husband Ralph Bates (in his last Hammer film) as well as headmaster Peter Cushing and his frosty wife Joan Collins (in her only Hammer film).