“It would seem a natural thing to do, unless the girl had been so cowed by threats of punishment or even torture if she made any outcry when allowed to go for a walk. I’m visualizing that girl as kept in close confinement, but not in any want or discomfort. She is most likely treated well as to food, rooms and all that, but is not allowed to step out of doors except with a strict guard and under some terrible penalty if she attempts to make herself known. With Betty’s love of fresh air and sunshine she would agree to almost anything to get out of doors. Then, too, if she merely formed those words without sound, the chance of their being read by a lip reader was really greater than the chance of doing any good by crying out aloud. “Had she done that, whoever had her in charge would have whisked her away at once, and no one would have paid any attention to the slight disturbance.” “It’s all perfectly logical and, oh, I hope Rodney gets some clue to the place where the picture was taken.” “I hope so, Ziz, but they’ve probably moved Betty away from there by now.” “Did you find out, Penny, what that stain on my frock was?” “I did.” “Well?” “Yes, my dear, you’ve struck it! You got that stain while you were down the well.” “Oh,” Zizi’s eyes lighted up; “of course I did! Those damp, mossy stones. And, then, oh, Wise one, just how did the same stain get on Martha’s hand?” “That, Zizi,” Wise spoke almost solemnly, “is part of the solution of the whole great mystery.” CHAPTER XVIII The Trap In a small but powerful motor boat Wise went on his voyage of exploration. The man who managed the craft was a stolid, silent person who obeyed Wise’s orders without comment. But when the detective directed that he go round the base of the headland, and skirt close to the rocks he grumbled at the danger. “Be careful of the danger,” Wise said, “steer clear of hidden reefs, but go close to the overhanging cliff, there where I’m pointing.” Skirting the cliff, at last Wise discovered what he was looking for, a small cave, worn in the rock by the sea. The floor of this cave rose sharply and it was with difficulty that Wise managed to scramble from the boat to a secure footing on the slippery wet rocks. “Look out there,” said the imperturbable boatman, “you’ll get caught in there when the tide comes up. I never noticed that hole in the wall before, it must be out o’ sight ’ceptin’ at low tide.” “Stay where you are and wait for me,” Wise directed, “if I’m not out here again in half an hour, go on home. But I’ll probably be back in less than that.” “You will, if you’re back at all! The tide will turn in fifteen minutes and in half an hour it’ll be all you can do to get out!”