When Brown, Mrs McCarthy and Bunty attend a private academy's annual ballroom competition, sergeant Goodfellow is 'found out' dancing as a hobby when debutante contestant Lucy Dawes is fatally stabbed. 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 was the doing of the socialite host, Lady Rose, having recognized her walking cane. A necklace Lucy was wearing is missing and Inspector Mallory arrests Lucy's fiance Oliver, who is found in possession of it. Father Brown thinks the answer lies back when Alexander was blinded when pushed downstairs during an alleged robbery without proper loot from such rich pickings or Rose's rumored love child. To continue his investigation Brown, McCarthy and Bunty join the competition, the latter as smitten Alexander's partner.
—KGF Vissers