access to the safe and could have copied the plans at any time. The prime suspect is Mrs Conroy, whose past life is something of a mystery, and she moves in diplomatic circles. She was specifically asked down for the weekend so that they could keep an eye on her. Questioning Conroy's foreign maid, Poirot correctly guesses that she screamed when Leonard Weardale sneaked an unexpected kiss from her. She quickly invented the ghost story when her cry attracted Fitzroy's attention. At this juncture, Lady Weardale reappears and asks Poirot if the matter could be dropped if the plans were returned. He agrees that that could be arranged and she promises that they will be within ten minutes. Poirot puts this offer to Lord Alloway, without mentioning any names, and leaves. Hastings questions this unexpected turn of events, suspecting Lady Weardale's rumoured bridge debts are real. Poirot points out that as the story of the shadow of an intruder leaving the study turned out to be incorrect, the plans must have been taken by Fitzroy or by Lord Alloway himself – the logical conclusion. Hastings is dubious but Poirot points out that the man was rumoured to be involved in share scandals years before, although he was later exonerated. Supposing the rumours were true, and he was being blackmailed, in all probability by Mrs Conroy, a foreign agent. He would hand over fake copies of the plans with suitable adjustments to make them useless, and then pretend they had been stolen. That would be why he insisted his loyal secretary was not suspected. Leonard Weardale was busy with the maid at the time of the supposed theft and Lady Weardale could not be the thief as she needed ten minutes to get the plans back, whereas she would need a lot less time if she had taken them and hidden them. Poirot's theory also explains why Lord Alloway did not want the guests told of the theft of the plans – he wanted the foreign power to receive the false plans. Hastings remains unconvinced. However, on the day when Lord Alloway became Prime Minister, Poirot receives a cheque and a signed photograph dedicated to "my discreet friend". He also hears that a foreign power attempted to build their own version of the submarine which ended up a failure. This short story was later expanded into the novella-length story The Incredible