“Also, because,” Wise went on, “because, I’m sure that is the footprint of the would-be burglar, and while the footprint as a print is too indistinct to be a clue to the man who made it, yet the dust that forms the print is indicative. It is a fine dust made up of particles of cement. I mean such dust as would adhere to a shoe that had traversed a cement floor, and, more likely an imperfect cement floor.” “That means the cellar!” Rodney cried; “I’ve been down there a lot of late, poking around for that everlasting secret passage, and there’s a lot of loose cement.” Wise gave him a quick glance, but his enthusiasm was so genuine, that the detective dismissed a sudden qualm of suspicion. “Slip down and get me a sample, will you?” he said, and Granniss went at once. “Big case, Zizi,” Wise said, as the two were left alone. But he spoke heavily, almost despairingly, and with no show of his usual exultant interest in a big case. “Yes, but,” the black eyes turned hopefully to his own, “there are tangible clues. And those of Betty’s can wait. Do you chase those that have to do with Martha first.” “I certainly shall. Martha was killed by the burglar. Did he kidnap Betty?” “And kill Mr Varian?” Zizi added, and then Granniss returned. He brought a little cellar floor dust in a paper, and, as Wise had expected, that and the particles he had scraped from the library rug, were indubitably the same. “Well, then,” Wise remarked, “the burglar came up from the cellar.” “Where he had been hiding, goodness knows how long!” Rodney exclaimed. “For we locked the house securely before we went upstairs.” “I think it’s time I took a look at the cellar,” said Wise, and all three started down. CHAPTER XII A Letter from Nowhere Pennington Wise himself assisted in the locking up of the house that night, for he was determined if any more burglars came, he would know how they got in. The money that Minna had in her possession he took charge of, saying he would be responsible for its safety. Long the detective lay awake in his pleasant bedroom that overlooked the sea. He could hear the great waves tossing and breaking at the foot of the cliff and he couldn’t free his mind from a queer obsession to the effect that those waves held the secret of the mysteries of Headland House. “It’s too absurd,” he thought to himself in the darkness, “but I do feel that the whole matter is dependent in some way or other on the cliff and the sea.” Had he been asked to elucidate this more definitely he could not have done so. It was only a hunch,—but Wise’s hunches were often worthy of consideration, and he determined to go out on the sea in somebody’s boat when the morning came, and see if he could find any inspiration. When the morning came it brought a fresh surprise.