"In the seclusion of her room she opened and thoroughly searched the box, but found only the original will in which John Thaneford had been named the residuary legatee. The natural explanation would be that Francis Graeme had been prevented from carrying out his intention of making you his heir, and that no later instrument was in existence. In her devotion to John Thaneford's interests, it would now become necessary for her to get the despatch-box back in the library before the tragedy should be discovered and the room carefully examined. She found her opportunity when Doctor Marcy went to meet Betty, leaving Effingham on guard at the library door. You remember the darky telling us that she had a shawl on her arm, an obvious means of concealing such an object as the despatch-box. Then she took the master-key from him——"
"Why did she wait so long?" I interrupted. "She might never have had that chance."
"Well, at the first opening of the library door she may have been too unnerved to risk it. You recall that she fainted at the moment when Marcus, the house-boy, made the discovery of the body.
"In the second place the box is rather bulky, and she would have found great difficulty in placing it in position, under the alert and curious eyes of the servants. Finally, she may have had some thought of re-entering the room by means of the postern-door, which still remained unlocked."
"A desperate dernier ressort," I observed. "Somebody would have certainly seen her."
"Granted. Anyway Betty's arrival did give her a chance, and she was quick to take advantage of it.
"Well, that's my case," concluded Warriner. "How does it strike you?"
"It has its weak points."
"Who unlocked the library door when Doctor Marcy returned with my Cousin Betty?"