It was as we traveled up to town next day that Peace told me his story. I will set it down as briefly as may be.
"I soon came to the conclusion that Ford, whether dead or alive, was inside the grounds of Meudon Hall. If he had bolted, for some reason, by the way, which was perfectly incomprehensible, a man of his ability would not have left a broad trail across the centre of his lawn for all to see. There was, moreover, no trace of him that our men could ferret out at any station within reasonable distance. A motor was possible, but there were no marks of its presence next morning in the mud of the roads. That fact I learned from a curious groom who had aided in the search, and who, with a similar idea upon him, had carefully examined the highway at daybreak.
"When I clambered to the top of the wall I found that the snow upon the coping had been dislodged. I traced the marks, as you saw, for about a dozen yards. Where they ended I, too, dropped to the ground outside. There I made a remarkable discovery. Upon a little drift of snow that lay in the shallow ditch beneath were more footprints. But they were not those of Ford. They were the marks of long and narrow boots, which led into the road, where they were lost in the track of a flock of sheep that had been driven over it the day before.
"I took a careful measurement of those footprints. They might, of course, belong to some private investigator; but they gave me an idea. Could some man have walked across the lawn in Ford's boots, changed them to his own on the top of the wall, and so departed? Was it the desire of someone to let it be supposed that Ford had run away?
"When I examined Ford's private rooms I was even more fortunate. From the boot-boy I discovered that the master had three pairs of shooting boots. There were three pairs in the stand. Some one had made a very serious mistake. Instead of hiding the pair he had used on the lawn, he had returned them to their place. The trick was becoming evident. But where was Ford? In the house or grounds, dead or alive, but where?
"I was able, through my friend the boot-boy, to examine the boots on the night of our arrival. My measurements corresponded with those that Jackson, the valet, wore. Was he acting for himself, or was Harbord, or even Ransome, in the secret? That, too, it was necessary to discover before I showed my hand.
"Your story of Harbord's midnight excursion supplied a clue. The secretary had evidently followed some man who had disappeared mysteriously. Could there be the entrance to a secret chamber in that corridor? That would explain the mystification of Harbord as well as the disappearance of Silas Ford. If so, Harbord was not involved.
"If Ford were held a prisoner he must be fed. His jailer must of necessity remain in the house. But the trap I set in the suggested journey to town was an experiment singularly unsuccessful, for all the three men I desired to test refused. However, if I were right about the secret chamber I could checkmate the blackmailer by keeping a watch on him from your room, which commanded the line of communications. But Jackson was clever enough to leave his victualing to the night-time. I scattered the flour to try the result of that ancient trick. It was successful. That is all. Do you follow me?"
"Yes," said I; "but how did Jackson come to know the secret hiding place?"
"He has long been a servant of the house. You had better ask his old master."