Towards the end of the First World War, Hastings calls on Hercule Poirot in his rooms to discuss the sensational news of the day - no less than the attempted assassination of the Prime Minister, David McAdam. Soon they are interrupted by two important visitors; Lord Estair, Leader of the House of Commons and Bernard Dodge, a member of theWar Cabinet. They enlist Poirot for help with a national crisis – the Prime Minister has been kidnapped. He was on his way to a secret peace conference to be held the next day at Versailles. He arrived in Boulogne-sur-Mer where he was met by what was thought to be his official car but it was a substitute. The real car was found in a side road with its driver, an ADC bound and gagged. As they tell Poirot the details, news reaches them by special courier that the bogus car has now been found abandoned and containing Captain Daniels, the Prime Minister’s secretary, chloroformed and gagged. His employer is still missing. Poirot wants to know the full details of the shooting that took place earlier and is told it occurred on the way back from Windsor Castle when, accompanied again by Captain Daniels and the chauffeur, Murphy, the car took a side road and was surrounded by masked men. Murphy stopped and one them shot at the P.M., but only grazing his cheek. Murphy shot off, leaving the would-be murderers behind. The P.M. then stopped off at a small cottage hospital to have his wound bandaged and then went straight on to Charing Cross Station to get the Dover train. Murphy has also disappeared, the P.M.’s car being found outside a Soho restaurant frequented by suspected German agents. As Poirot packs to leave for France he voices his suspicions of both Captain Daniels and Murphy and wonders why such a melodramatic event as "shooting by masked men" took place before the kidnap. Poirot goes over the channel with various detectives involved in the case, among them Inspector Japp. Once in Boulogne he refuses to join in the search but sits in his hotel room and thinks for several hours, using the "little grey cells". Suddenly seeing daylight he returns back to Britain where, in an official car, he begins a tour of cottage hospitals to the west of London. They then call at a house in Hampstead, the police raid it and recover both Murphy and the Prime Minister. The villain of the piece was Daniels who kidnapped both men in the shooting, taking to London substitutes with the "P.M.’s" face disguised by bandages from a shooting that, in fact, had never occurred and Poirot’s search of the cottage hospitals proved that no one’s face was bandaged up that day. The "kidnap" then took place in France, leaving the investigation concentrated there when the real P.M. had never left the country. Captain Daniels was known to have a "sister" near Hampstead but she is in fact Frau Bertha Ebenthal, a German spy who Poirot has been searching for some time. The real Prime Minister is whisked of to Versailles for the conference.

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