"But surely Miss Howard had ample opportunities of aiding him."
"Yes, but Miss Howard did not know of the paper's existence. In accordance with their prearranged plan, she never spoke to Alfred Inglethorp. They were supposed to be deadly enemies, and until John Cavendish was safely convicted they neither of them dared risk a meeting. Of course I had a watch kept on Mr. Inglethorp, hoping that sooner or later he would lead me to the hiding-place. But he was too clever to take any chances. The paper was safe where it was; since no one had thought of looking there in the first week, it was not likely they would do so afterwards. But for your lucky remark, we might never have been able to bring him to justice."
"I understand that now; but when did you first begin to suspect Miss Howard?"
"When I discovered that she had told a lie at the inquest about the letter she had received from Mrs. Inglethorp."
"Why, what was there to lie about?"
"You saw that letter? Do you recall its general appearance?"
"Yes--more or less."
"You will recollect, then, that Mrs. Inglethorp wrote a very distinctive hand, and left large clear spaces between her words. But if you look at the date at the top of the letter you will notice that 'July 17th' is quite different in this respect. Do you see what I mean?"
"No," I confessed, "I don't."
"You do not see that that letter was not written on the 17th, but on the 7th--the day after Miss Howard's departure? The '1' was written in before the '7' to turn it into the '17th'."
"But why?"
"That is exactly what I asked myself. Why does Miss Howard suppress the letter written on the 17th, and produce this faked one instead? Because she did not wish to show the letter of the 17th. Why, again? And at once a suspicion dawned in my mind. You will remember my saying that it was wise to beware of people who were not telling you the truth."
"And yet," I cried indignantly, "after that, you gave me two reasons why Miss Howard could not have committed the crime!"
"And very good reasons too," replied Poirot. "For a long time they were a stumbling-block to me until I remembered a very significant fact: that she and Alfred Inglethorp were cousins. She could not have committed the crime single-handed, but the reasons against that did not debar her from being an accomplice. And, then, there was that rather over-vehement hatred of hers! It concealed a very opposite emotion. There was, undoubtedly, a tie of passion between them long before he came to Styles. They had already arranged their infamous plot--that he should marry this rich, but rather foolish old lady, induce her to make a will leaving her money to him, and then gain their ends by a very cleverly conceived crime. If all had gone as they planned, they would probably have left England, and lived together on their poor victim's money.