Lady Felicia knows the Hollywood star Rex Bishop who is in Kembleford filming a "B" movie The Brides of the Demon. He invites Father Brown and Mrs McCarthy, a fan of Bishop, to view the filming. Tensions are evident between the film's participants, the director, his actress wife, a starlet, Rex Bishop, and the writer. The director is found dead wearing a demon's mask and Inspector Mallory does not appreciate Father Brown's help.