Accompanied by Poirot, Inspector Japp is visiting Brussels where he is to receive the "Branche d'Or" for his services to Belgium. A remark of Commissaire de Police Chantalier brings back memories of a case which Poirot "failed" to solve more than 20 years ago. The very notion is plainly ridiculous - and Poirot amusedly turns over in his mind the fascinating story of the liberal politician and his fateful chocolate box.