"But what could he possibly gain by that?" Jack asked.
"Well, you see, I had let him know that I was quite alone in the business," said Bates. "At the same time, he was not aware that my information was so complete. If he could murder me and get safe home without being detected, he was in a position to prove an absolute alibi. Of course, I did not dream that I was running any risk of my life--but that is not the point. You will remember my suggesting to you yesterday the advisability of you dining in Panton Square last night. I suppose that was all right?"
Jack replied that he had followed Bates's instructions out implicitly. He had done all he could in that way.
"Very well, then. You see what I am driving at. I take it for granted that Anstruther's mysterious musical friend was much in evidence last night. I have no doubt that Miss Helmsley and yourself listened with rapt attention to the music in the study."
"We had every opportunity of doing so," Jack said.
"That is precisely what I expected. Anstruther must have left the house a little after ten o'clock, and I don't see how it was possible for him to return much before half-past twelve. I suppose you didn't happen to see him when he came in?"
"Indeed I did," Jack said. "It was quite half-past twelve when I was leaving the house. The music was still in progress, but when I slipped out of the front door, Anstruther was rapidly approaching the house running across the lawn. He seemed very much annoyed and put out when he saw me, and muttered something to the effect that he had heard somebody trying the front door. I understood him to say that he had not been out all the evening, but that was all nonsense. I could see by his boots that he had been walking some considerable distance. Of course, you see what the dodge is: he does not leave the house by the door, but by the French window leading from the study to the garden. This window he leaves unfastened, so that he can get back at any time without a soul being any the wiser. Of course, there was always a chance of somebody finding the window unlatched, but that is a small matter."
"Is the window always left open?" Bates asked thoughtfully.
Jack replied that he thought so. Bates smiled with the air of a man who is perfectly well satisfied.
"I am going to get up presently," he said. "After I have had a bath and some tea, I shall be quite fit for duty again. I want you to find some pretext for calling at Anstruther's just after dinner, because I may need your assistance."