There was a dead silence for a minute and a half.
Then I laughed.
“You’re mad,” I said.
“No,” said Poirot placidly. “I am not mad. It was the little discrepancy in time that first drew my attention to you—right at the beginning.”
“Discrepancy in time?” I queried, puzzled.
“But yes. You will remember that every one agreed—you yourself included—that it took five minutes to walk from the lodge to the house—less if you took the short cut to the terrace. But you left the house at ten minutes to nine—both by your own statement and that of Parker, and yet it was nine o’clock as you passed through the lodge gates. It was a chilly night—not an evening a man would be inclined to dawdle; why had you taken ten minutes to do a five-minutes’ walk? All along I realized that we had only your statement for it that the study window was ever fastened. Ackroyd asked you if you had done so—he never looked to see. Supposing, then, that the study window was unfastened? Would there be time in that ten minutes for you to run round the outside of the house, change your shoes, climb in through the window, kill Ackroyd, and get to the gate by nine299 o’clock? I decided against that theory since in all probability a man as nervous as Ackroyd was that night would hear you climbing in, and then there would have been a struggle. But supposing that you killed Ackroyd before you left—as you were standing beside his chair? Then you go out of the front door, run round to the summer-house, take Ralph Paton’s shoes out of the bag you brought up with you that night, slip them on, walk through the mud in them, and leave prints on the window ledge, you climb in, lock the study door on the inside, run back to the summer-house, change back into your own shoes, and race down to the gate. (I went through similar actions the other day, when you were with Mrs. Ackroyd—it took ten minutes exactly.) Then home—and an alibi—since you had timed the dictaphone for half-past nine.”