“Now there were two pointers toward the murderer of Meadows, both somewhat vague—motive and aconitine. Assuming, as I think one had every right to do, that Meadows would not have shrinked from blackmail, the first of these was so wide that I shelved it for a time and concentrated on the second. This was wide too, but it could be narrowed down. If one took the working assumption that the aconitine had come from Dr. Vane’s laboratory, there were, excluding servants and so on, three people who could have got hold of it: Dr. Vane himself, Miss Williamson and Miss Cross. Well, for some reason or other (psychological again) I wasn’t drawn toward Dr. Vane as the murderer although, as you showed, Inspector, it was possible to make out a pretty convincing case against him—probably because you had gone out of your way to make a pretty convincing case against him, perhaps. In the same way, of course, I had already discarded Miss Cross. There remained Miss Williamson.
“Well, Miss Williamson was a difficulty. Why in the name of goodness should she want to kill Meadows? I could see no possible reason. There would have been a reason, of course, if she had already murdered Mrs. Vane—an idea that had already occurred to me by the way, Inspector, and for the same motive, before you put it forward once as a joke, if you remember. There would have been a motive in that case, if Meadows had seen her do it; but I was working on the theory that he had murdered Mrs. Vane himself. For the life of me I couldn’t see, if that were the case, how she could possibly be his murderess.”
“Out of the question, I should have said,” interjected the inspector.
“Yes, that’s what I decided. Well, there were all my three suspects discharged without a stain on their characters; so I was driven to the conclusion that either the aconitine had not come from Dr. Vane’s laboratory at all, or else Meadows had not killed Mrs. Vane. In either case I was in an impasse and had to go back a little way. I went back to motive.
“Now this is where we really do begin to warm up. Do you remember last night, Inspector, you asked me who had the biggest motive for wanting Meadows out of the way, and I replied, somewhat facetiously, that Mrs. Vane had? I began to play with that idea.”
“Mrs. Vane?” repeated Anthony incredulously. “But she was dead already.”
“When Meadows died, yes; but she had plenty of motive, I imagine, for wanting him out of the way before she died herself. Anyhow you see the idea. I was asking myself, with growing excitement: was there any way in which Mrs. Vane could have brought about Meadows’ death, although she herself was already dead? And the answer, of course, was obvious. Yes, there was!” Roger leaned back in his chair and beamed triumphantly at his audience.
“This is very clever, Mr. Sheringham,” said the inspector ungrudgingly. “Very clever indeed. Yes, I see now what you’re driving at, but let’s have it in your own words.”
“Well, as you probably discovered yourself, Meadows had had no visitors during the last few weeks, so far as the landlady knew. Any theory, then, which was to cover the insertion of poison in his tobacco must presuppose the murderer’s visit late at night and, probably, through the sitting-room window, with or without Meadows’ own knowledge. But on the night before the murder the landlady, although awake, heard no sounds at all, whereas she had heard a visitor’s voice, quite distinctly, some three weeks beforehand, that visitor being proved to be Mrs. Vane.”
“Wait a minute, sir,” said the inspector. “What’s all this about? I don’t know anything of a visit of Mrs. Vane’s.”