Surely you do yourself an injustice. One more coruscation, my dear Watson – yet another brain-wave! Had the volume been an unusual one, he would have sent it to me. Instead of that, he had intended, before his plans were nipped, to send me the clue in this envelope. He says so in his note. This would seem to indicate that the book is one which he thought I would have no difficulty in finding for myself. He had it – and he imagined that I would have it, too. In short, Watson, it is a very common book."