The Incredible Theft

A wealthy industrialist lays a trap to catch a German sympathiser, and the whole scheme backfires when the plans for a new fighter plane vanish instead. Espionage is the obvious answer, and Poirot is suspicious of the obvious. The theft is too convenient, too clean. But the question of who benefits points away from the enemy and toward the drawing room, and Poirot suspects from the start that the disappearance is a family matter wearing a spy's coat.

The case moves among the Mayfields and the Carringtons: Tommy Mayfield, the ambitious Mrs Vanderlyn, Lady Mayfield, Sir George Carrington and his wife, and young Reggie Carrington. Everyone had access to the plans and everyone has a reason to want them gone, and the hunt for a spy slowly turns into a hunt for something closer to home. The house party atmosphere keeps the manners polished and the motives buried. The country house setting gives the theft an audience, and the audience is full of suspects. Hastings is scandalised, which is roughly his job, and Japp keeps expecting an act of straightforward treason to appear.

David Reid, Clive Exton and Agatha Christie share the writing credit, with Edward Bennett directing. John Stride plays Tommy Mayfield, Carmen Du Sautoy is Mrs Vanderlyn, Ciaran Madden plays Lady Mayfield, John Carson is Sir George Carrington, Phyllida Law plays Lady Carrington and Guy Scantlebury is Reggie Carrington. David Suchet, Hugh Fraser, Philip Jackson and Pauline Moran hold the centre. It went out on 26 February 1989.

There is a pleasing twist in the way the episode borrows the language of wartime espionage and then points out that people will steal for smaller reasons than patriotism. The fighter plane matters less than the person holding the blueprints, and Poirot knows which end of the theft to look at. Industrial secrets, it turns out, are easier to misplace than people. The episode keeps its powder dry until the final act, and the reveal lands with a thump.