Disappearing, Wise began his climb up the floor of the cave, and at a point just above high water there was a fissure in the cliff which admitted air and some light. At this point the cave ran back for some distance, though still on a rising level. During the winter storms the ocean evidently had worn this tunnel in the rock. Wise at once realized that this nature-made tunnel ran on for some distance until it ended in the old well. Using his flashlight when necessary, he made his way, until he reached the pile of stones which he himself had pushed out from the well and found to his satisfaction that he had indeed come to the well, and that his solution of the mystery of a secret passage into Headland House was accomplished. But what a solution! The difficulty and danger of entrance or exit by means of that rock tunnel and that old well could scarce be exaggerated! Moreover, all such entrances or exits must be made at the lowest ebb of the tide. But the cave was roomy, not uncomfortable, and the tunnel, though cramped in places, was fairly navigable. There was plenty of room in the cave quite above reach of the highest tide, and the whole matter was clear and simple now that he saw it all, but he marveled at the energy and enterprise that could conceive, plan and carry out the various attacks. Whoever the criminal, or the master criminal, might be, he had come up through that tunnel and well on the several occasions of the kidnapping of Betty, the murder of Martha, the abduction of North,—yes,—and Wise remembered the letter that had been mysteriously left on the hall table,—also the night the library had been entered,—clearly, the man came and went at will! A master mind, Wise concluded, he had to deal with, and he set his own best energies to work on his problems. The way between Headland House and the outer world was not easy of negotiation, but it was a way, and it was passable to a determined human being. Wise was back inside the prescribed half hour, and the uninterested boatman took him back to the Harbor without question or comment as to his enterprise. That afternoon, Wise called Minna and Doctor Varian into the library and closed the door. Zizi was also present, her black eyes shining with anticipation, for she knew from Wise’s manner and expression that he was making progress, and was about to disclose his discoveries. “I have learned a great deal,” the detective began, “but not all. At least, I have found the so-called secret passage, which we all felt sure must exist.” He described the cave and the tunnel as he had found them, and the outlet into the old well, so carefully piled with loose stones that it would escape the observance of almost any searcher. He told briefly but graphically of his exit from the well for a distance, and of his later entrance from the cave and his procedure to the well.