A chance encounter at a roadside café reunites the observant Mr. Satterthwaite with the enigmatic Mr. Harley Quin, triggering a complex investigation into a family's hidden history. While awaiting repairs for his vehicle, Satterthwaite finds himself drawn into a conversation that pivots on a single, cryptic word: 'Daltonism.' He must navigate the social intricacies of a local family and the mysterious influence of his companion to uncover the truth behind a series of events involving a set of harlequin china. The narrative unfolds through a blend of observational dialogue and the characteristic atmospheric tension found in Christie's short-form mysteries.

This story is regarded as a quintessential example of Christie's ability to weave supernatural-adjacent atmosphere into a grounded mystery. Readers often highlight the charm of the Satterthwaite and Quin pairing, noting how their dynamic provides a unique lens through which to view human folly. The brevity of the piece is frequently praised for its efficiency, as it delivers a complete puzzle without the need for extensive exposition. The inclusion of the 'Daltonism' clue is often cited as a clever mechanism that rewards the attentive reader, solidifying the work's status as a polished entry in the author's extensive bibliography.