“That settles it,” cried Dorothy. “I’m sure I know how he opened his secret closet or closets. You remember the insulated wire covering they found, when they came in after the doctor’s death.” We nodded eagerly. “That was the winding of an electro-magnet. He attached it to the long flexible cord of that incandescent light socket in the anteroom, took it in, opened his closets, brought it out again, and went back. See if you can find an electro-magnet in the cases or the storeroom, and we’ll open things up.” Scarcely were the words out of her mouth, before Swenton had hurried to a drawer, and pulled out three small electro-magnets, all of the same size. “Here are the only ones I know of, in the laboratory,” he exclaimed. “I can connect one of them with the flexible cord in a minute. We shall want more light, though. If one of you gentlemen will get another connector and fix it to a socket, I’ll fit the magnet. You’ll find some connectors for that size socket in the storeroom, I’m sure.” With four practised hands at work, it was scarce ten minutes before an incandescent stood on the table in the inner room, while we had an electric magnet connected to a long flexible cord which brought current from an incandescent light socket in the next room. Dorothy stood in the centre, once more in command. “I believe it’s under one of those pegs,” she said. “See what’s under them.” Round and round the room we went, pulling at every peg that joined the sealed walls. Under each was a nail. Tom picked up one of the pegs as we drew it forth. “Humph!” he cried. “Insulated by caema. That explains why the nails were left. What a careful job this was, anyway.” Hamerly and Swenton nodded. I started to ask what caema was, but I was pulling on a particularly refractory peg just then and let it go. The word stuck fast in my memory, however. It was the same one I had seen in Tom’s book on our journey up from Portsmouth. As each peg came out, the little electro-magnet was brought up to the hole and its action watched. Not a nail stirred. We had gone around three sides of the room, when Tom called out, “This peg came easily. Bring over the magnet.” Before I could bring the magnet within an inch of the hole, the nail within sprang out and attached itself to the magnet, just as a needle springs up and clings to the horseshoe magnet of a child. As it sprung, the whole panel, four feet high and three feet across, opened on easy hinges and swung outward, showing a small inner door. Tom gave a long, low whistle. “Right again, sister,” he remarked. “What should we do without you?” The stout oak door, strong as it was, proved no obstacle to our attack, and readily swung outward. Stooping, we peered within. Empty shelves on one side. A row of drawers on the other. One by one we drew the drawers from their places. Every one was empty. From top to bottom of the recess we searched, but without avail. Finally we straightened up with blank faces.