Father Brown , Mrs McCarthy, and Bunty attend a ballroom competition and one of the contestants, Lucy Dawes, is murdered; her blind dancing partner Alexander Walgrave, who found the body, believes he knows who the murderer is and asks Father Brown and Bunty prove it. A necklace Lucy was wearing is missing and Inspector Mallory arrests Lucy's fiancé Oliver when he is found in possession of it. Father Brown realises the answer lies some time ago when Alexander was blinded when pushed downstairs. To continue his investigation Brown, McCarthy and Bunty join the competition.