“There’s only one thing against it,” I said slowly. “If Ackroyd went on reading that letter as soon as I left, as he intended to do, I don’t see him continuing to sit on here and turn things over in his mind for another hour. He’d have had Parker in at once, accused him then and there, and there would have been a fine old uproar. Remember, Ackroyd was a man of choleric temper.”

“Mightn’t have had time to go on with the letter just then,” suggested the inspector. “We know someone was with him at half-past-nine. If that visitor turned up as soon as you left, and after he went, Miss Ackroyd came in to say good night⁠—well, he wouldn’t be able to go on with the letter until close upon ten o’clock.”

“And the telephone call?”

“Parker sent that all right⁠—perhaps before he thought of the locked door and open window. Then he changed his mind⁠—or got in a panic⁠—and decided to deny all knowledge of it. That was it, depend upon it.”

“Ye‑es,” I said rather doubtfully.