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."
"My dear Poirot," I said in a voice that sounded strange and forced to my own ears, "you've been brooding over this case too long. What on earth had I to gain by murdering Ackroyd?"
"Safety. It was you who blackmailed Mrs. Ferrars. Who could have had a better knowledge of what killed Mr. Ferrars than the doctor who was attending him? When you spoke to me that first day in the garden, you mentioned a legacy received about a year ago. I have been unable to discover any trace of a legacy. You had to invent some way of accounting for Mrs. Ferrars's twenty thousand pounds. It has not done you much good. You lost most of it in speculation—then you put the screw on too hard, and Mrs. Ferrars took a way out
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