"Why did you think that?"
"Because he knew where the key was. I took it out of my pocket when we were alone in the smoking-room before going up to bed, and asked him what I should do with it.
"'Oh, put it in a drawer,' he said, pointing to the writing-table, and I put it there, as he suggested. Of course I see now that some one else may have found the key in that drawer, but at first it did look as if David must, for some reason, have taken it, and been in the library, after I'd gone to bed."
"It seems very unlikely that anyone else would have hit on the place where you had put it," said Gimblet reflectively. "And if they had done so, would they have recognized the key? Is the library key peculiar in any way?"
"It is rather an uncommon pattern," said Mark. "It is very old and strong. I think anyone who knew the key would have recognized it all right."
"It is hardly likely that anyone would have found it if they had had to search all through the house for it in the middle of the night," commented Gimblet. "Is there no other way of getting into the library?"
"No, there is only one door."
"How about the window? It was broken; could not anyone have put in a hand, or raised the sash?"
"I don't think anyone could have got in. It isn't a sash window. There are stone mullions and small leaded casements in the old part of the castle where the library is, and I doubt if anyone larger than a child could squeeze through; in fact, a child couldn't; there are iron bars down the middle, which make it too narrow."
"H'm," murmured Gimblet. "I should like to have a look at them. And what was the doctor's report?"
"He said that the injuries to the heart were such that death must have been instantaneous, or practically so."
"Did anything else come out?"
"Nothing, except the evidence against poor old David, I'm sorry to say."
"You haven't told me that yet," said Gimblet. "Go on from when the police arrived on the scene."
"As soon as it was daylight we started off again on our search. But right at the beginning of it, they came upon the footsteps."
"Ah, where were they?"