When Burnley glanced over this melancholy epistle it seemed at first merely to indicate that Felix was no better than he might be, and it was not till he had read it again that its immense significance struck him. What if this paper supplied the motive of the murder? What if it had opened to Mme. Boirac a chapter in Felix’s life which otherwise would have remained closed, and which he intended should remain closed? As Burnley thought over it he believed he could at least dimly reconstruct the scene. Felix and Madame had arrived at St. Malo, and then in some way, by some act of extraordinary carelessness on Felix’s part, she got hold of the letter. A quarrel would be inevitable. What would Felix do? Probably first snatch the letter from her and thrust it into his pocket out of sight. Then, perhaps, try to pacify the angry lady, and, finding this impossible, the quarrel would get worse and worse till finally in a paroxysm of passion he would seize her throat and choke out her life. The murder committed, he would be so upset that he would quite probably forget all about the letter. The oversights of criminals were notorious. The more the Inspector considered the matter, the more likely his theory seemed. But here again he had to recognise it was entirely surmise. No proof that this had taken place was forthcoming. It was another case of the thus-far-and-no-farther evidence he had been deploring in the train. At all events it suggested another line of inquiry. This girl must be found and the relations between her and Felix gone into. Burnley foresaw much arduous work in front of him. At length he put the letter away in his notebook, and the search continued. Finally, as it was beginning to get dusk, every room had been done except the study where Felix and the Inspector had had their midnight discussion. ‘I think we had better come back to-morrow,’ said Burnley. ‘There’s no use in searching by lamplight.’ Accordingly, the next morning saw them again at work. They crawled over the floor so as to get every part of the carpet between themselves and the light, but could find no impressions. They peered with their lenses in the pile of the carpet, they felt between the arms and seats of the padded leathern chairs, all to no purpose. And then Burnley made his second discovery. Between the study and the dining-room adjoining there was a door, evidently unused, as it was locked and the key was gone. On the study side this door was covered by a heavy curtain of dark-green plush. In front of the curtain, and standing with its back to it, was a small chair whose low, leather-padded back formed a half-circle with the arms. In his anxiety to leave no part of the carpet unexamined, Burnley had moved this chair aside.