Here the handiwork of man was in evidence. He was ascending into a space that had been hollowed out of the heart of a tree. Above his head was a small wooden trapdoor held in place by a wood slide or bolt. Releasing the bolt allowed the door to drop silently downward on hinges formed of stiff leather. A package fell into his hands, followed by a draft of air laden with the scent of summer woods. Pushing up his light Forrester recognized the hollow in the oak tree. He saw also that the upper side of the trapdoor was so prepared that it would seem like part of the tree to anyone investigating from above. At last the most vital secret of the "Friends of the Poor" was in his hands—the method by which they had so mysteriously secured their toll under the very eyes of the detectives. Forrester examined the small, flat package in his hand. Someone had placed a contribution in the tree that night. Then Forrester shivered. The scoundrels would come to collect at any moment! He was shut in at the far end of a narrow passage, the only way of escape leading back through the cottage where they would enter. If they met him here his end would be sure and his disappearance a mystery forever. Hastily he climbed down the ladder and was about to go when several objects drew his attention. The temptation to investigate these before he left was too strong to resist and Forrester lingered a moment or two longer. All the paraphernalia that had made possible the ghostly illusions, which had frightened others and puzzled him, now lay revealed as nothing but mean claptrap. On the wall hung a group of rusty chains, a small megaphone for throwing the voice and an old locomotive bell. In one corner stood a tin similar to a paint can. This, Forrester found, contained a preparation commonly known as phosphorescent paint and a nearby glove, which smelled strongly of the substance, solved the riddle of the flaming hand which had impressed even the phlegmatic Green. The greatest curiosity of all, however, was a black tube standing against the wall. Forrester instantly remembered the appearance of something of this kind in Humphrey’s photograph. On examination it proved to be a homemade periscope. By pushing it up into the opening in the oak tree it was probably possible for a person in the cave to ascertain what was occurring on the surface. Forrester did not wait to experiment, for he was sure that on the night of the Italians’ visit someone was taking in the scene and the projecting end of the periscope had been picked up by the camera.