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The Incredible Theft is a novella by Agatha Christie which was an expansion of The Submarine Plans, an early short story first published in The Sketch in 1923 in the U.K. Much longer than its predecessor, The Incredible Theft was first published in 7 parts in the Daily Express from 6-12 April 1937. That same year, the novella was gathered and published as part of the anthology Murder in the Mews and Other Stories in the U.K. The U.S. version of Mews did not contain The Incredible Theft when first published there in 1937 but was included in a later edition in 1987.


Poirot is summoned urgently to help recover the plans of a revolutionary new bomber which had been stolen. The plot is very similar to The Submarine Plans. The text is longer, with more details, the character names have been changed and the plans, originally that of a submarine, have been changed to that of a bomber aircraft.

Plot summary

(may contain spoilers - click on expand to read)

A house party is taking place at the home of Lord Charles Mayfield, a self-made millionaire whose riches come from his engineering prowess. With him are Air Marshal Sir George Carrington, his wife and son, Lady Julia and Reggie, a Mrs Vanderlyn, a beautiful blonde American woman and Mrs Macatta, a forthright MP. They are joined for dinner by Mr Carlile, Mayfield's secretary. The real reason for the house party becomes obvious when the women, Reggie and Carlile retire from the dinner table: Lord Mayfield and Sir George are there to discuss the plans for a revolutionary new bomber plane that will give Britain supremacy in the air. The two men also discuss Mrs Vanderlyn – she has been involved in some dubious spying and espionage in which she uses her charms to seduce her victims into telling her their secrets. Mayfield has invited her to his house to tempt her with something big – the plans of the bomber – in order to trap her once and for all.

That evening, after their bridge game, all of the guests retire for bed except, again, Mayfield and Sir George. Mayfield asks Carlile take the plans for the bomber from the safe and place them in the study for the two men to peruse over. On the way, Mayfield and Sir George collide with Mrs Vanderlyn who says she has come down to retrieve her book. The two men take a turn on the terrace before getting down to work but Mayfield is startled when he says he caught a glimpse of a figure leaving the study by the French window although Sir George saw nothing. Returning to the study, Mr Carlile has got the papers out but Mayfield quickly sees that the plans of the bomber itself have gone. Carlile is questioned but he is adamant that they were in the safe and he put them on the table. He had been distracted for a moment when he heard a woman's scream in the hallway and running out found Leonie, Mrs Vanderlyn's maid, who claimed that she had seen a ghost. Aside from that, he never left the study. Mayfield is at a loss as to what to do next, so Sir George suggests calling in Hercule Poirot. Mayfield is reluctant at first but finally agrees.

Poirot arrives in the middle of the night. He is given the sequence of events and hears of the suspicions regarding Mrs Vanderlyn. Investigating the grass leading off the terrace, Poirot confirms that there are no footprints, which means that the theft was committed by someone in the house. After questioning Mayfield and Sir Charles, he retires for the night and continues questioning the ladies and Reggie the next morning. From this, he deduces that Leonie saw no ghost – she screamed because Reggie Carrington sneaked up on her and snatched a kiss.

Poirot suggests to Mayfield that he comes up with a pretext to bring the party to an end in order that his guests leave the house. During their departure, Lady Julia, takes Poirot aside and, having ascertained that the important thing was the return of the papers, offers to get them within twelve hours if no further action is taken. Poirot agrees to this. As Mrs Vanderlyn gets into her car, she sends Leonie back to fetch her dressing case which had been left in the hall. Mrs Vanderlyn then calls to Mayfield and asks him to help post a letter.

After all the guests depart, Poirot tells Mayfield he has solved the case. He knows where the plans are. Mayfield is surprised. Poirot goes through all the suspects. Lady Julia has offered to return the papers and talks like she knows who has the plans. She thinks Reggie has them. He is hard up for money, and had been infatuated by the attentions of Mrs Vanderlyn. Lady Julia must have gone to her son's room and found him missing although he said he had been in the room all night. Thought Reggie must have taken the plans at the behest of Mrs Vanderlyn but she in this she is mistaken. She doesn't know that her son was busy philandering with Leonie at the time and therefore cannot be the thief. Mrs Macatta was heard snoring in her room, Mrs Vanderlyn was heard to call for Leonie from upstairs so all of them are exonerated.

Only Carlile and Mayfield are the remaining suspects. Carlile had access to the safe at all times and could have taken tracings of the plans at his leisure, so only Mayfield is left. Poirot is sure that Mayfield had put the plans into his own pocket when going into the study. His motive is linked to an accusation some years earlier that he was had been involved in some negotiations with a belligerent foreign power which was highly unpopular. the government had publicly denied it but suppose the foreign power had some proof, some document? He could have been blackmailed for the plans of the bomber in exchange for the incriminating document. Mrs Vanderlyn had been appointed the agent in the transfer. The plans had gone into her dressing case and she had then returned Mayfield's incriminating document as a letter she wanted him to help post.

Mayfield confesses that Poirot's knowledge is complete. He must think that Mayfield had been a traitor. But Poirot doesn't think so. Mayfield was a talented engineer. There will be some subtle changes in the plans so that the foreign power will find the bomber a dismal failure. Mayfield says Poirot is much too clever. Mayfield believes he is needed to steer England through the coming world crisis he sees coming. He refused to be derailed by some personal matter in the past. Therefore he was forced to make the best of both worlds. That was the mark of a politician, Poirot states.


Film, TV, or theatrical versions

Agatha Christie's Poirot

A television film with David Suchet as Poirot was produced as episode 8 of Series 1 of the ITV series Agatha Christie's Poirot, first broadcast on 26 February 1989. Some slight changes were introduced but the basic premise of the story is unchanged. Some secret plans are stolen--in this case the plans for a fighter plane (portrayed by a Spitfire). MAyfield is a aircraft and arms industrialist instead of a government minister. In comic relief Poirot and Hastings have to 'borrow" one of Inspector Japp's police cars to give chase to Mrs Vanderlyn who is hurrying to hand over the stolen plans to the German embassy.

Publication history