The film was originally inspired by a conversation director Jess Franco had with jazz artist Chet Baker. Franco at first conceived the film as a bi-racial love story, but the distributors felt the idea wouldn't wash with audiences of the time so the story was re-written as a surreal thriller.
Jess Franco wanted the film to be titled "Black Angel" but distributors changed the title for marketing reasons and also altered the director's original ending.
Director Jess Franco once said he loved working with Dennis Price on this film because of Price's constant professionalism. The two would continue to work together on Franco's next films.
According to Jess Franco, star James Darren actually did fall in love with co-star Maria Rohm during the production, though it is unknown whether the two actually developed a relationship.