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.
As he stooped at the place where the chair had been, a bright object sticking to the curtain caught his eye. He looked more closely. A small, slightly bent, gold safety-pin, bearing a tiny row of diamonds, was caught in the braid at the top of the hem. The point had not penetrated, and the pin fell to the floor when Burnley touched the plush.
He picked it up.
‘That’s rather a fine thing even for a natty boy like Felix,’ he said as he showed it to Kelvin. And then he stood quite still as it flashed across his mind that here, perhaps, was another link in the chain that was being forged about Felix—a link possibly even more important than any of the foregoing. What if it did not belong to Felix at all? It looked too dainty and delicate for a man’s use. What if it was a lady’s? And, most important question of all, what if that lady was Mme. Boirac? If this proved true, his case was complete.
Dropping into the arm-chair he had occupied on the occasion of his midnight interview with Felix, he considered the possibilities opened up by his new discovery, endeavouring to evolve some theory of how a pin or brooch belonging to the deceased lady could have been dropped where he found this one. As he did so, a picture of what might have happened gradually grew in his mind. First, he thought it likely that a lady in evening dress would wear such a pin, and it might easily be at her neck or shoulder. And if she had sat in that chair with her back to the curtain, and any one had caught her by the throat and forced her head backwards, what could be more likely than that the pin should be pulled out in the struggle? And if it were pulled out it almost certainly would drop where or whereabouts he found it.