‘One thing did puzzle me—the motive. You were, I was convinced, an honest man, a man of integrity. That showed in your anxiety that no innocent person should be suspected. It was also obvious that the theft of the plans might easily affect your career unfavourably. Why, then, this wholly unreasonable theft? And at last the answer came to me. The crisis in your career, some years ago, the assurances given to the world by the Prime Minister that you had had no negotiations with the power in question. Suppose that that was not strictly true, that there remained some record—a letter, perhaps—showing that in actual fact you had done what you had publicly denied. Such a denial was necessary in the interests of public policy. But it is doubtful if the man in the street would see it that way. It might mean that at the moment when supreme power might be given into your hands, some stupid echo from the past would undo everything.

‘I suspect that that letter has been preserved in the hands of a certain government, that that government offered to trade with you—the letter in exchange for the plans of the new bomber. Some men would have refused. You—did not! You agreed. Mrs Vanderlyn was the agent in the matter. She came here by arrangement to make the exchange. You gave yourself away when you admitted that you had formed no definite stratagem for entrapping her. That admission made your reason for inviting her here incredibly weak.

‘You arranged the robbery. Pretended to see the thief on the terrace—thereby clearing Carlile of suspicion. Even if he had not left the room, the desk was so near the window that a thief might have taken the plans while Carlile was busy at the safe with his back turned. You walked over to the desk, took the plans and kept them on your own person until the moment when, by prearranged plan, you slipped them into Mrs Vanderlyn’s dressing-case. In return she handed you the fatal letter disguised as an unposted letter of her own.’

Poirot stopped.

Lord Mayfield said:

‘Your knowledge is very complete, M. Poirot. You must think me an unutterable skunk.’

Poirot made a quick gesture.

‘No, no, Lord Mayfield. I think, as I said, that you are a very clever man. It came to me suddenly as we talked here last night. You are a first-class engineer. There will be, I think, some subtle alterations in the specifications of that bomber, alterations done so skilfully that it will be difficult to grasp why the machine is not the success it ought to be. A certain foreign power will find the type a failure…It will be a disappointment to them, I am sure…’

Again there was a silence—then Lord Mayfield said:

‘You are much too clever, M. Poirot. I will only ask you to believe one thing. I have faith in myself. I believe that I am the man to guide England through the days of crisis that I see coming. If I did not honestly believe that I am needed by my country to steer the ship of state, I would not have done what I have done—made the best of both worlds—saved myself from disaster by a clever trick.’