"Now for the Trinity church-yard," he muttered, as he sprang toward the low wall at the point before which the strange woman had kneeled but a few moments before. "I've got a genuine mystery on my hands at last, I fancy, and that's what I've been sighing for these last three months---- Ha, Schneider, where's your prisoner? Surely you are not back from the station as soon as this?" The stout German policeman, panting for a breath, stood trembling by his side. "Dunder und blitzen! now mebbe you kills me, Mr. Hook. I swear it vos not my fault." "Not your fault! Have you lost your prisoner--but that is impossible! Speak, you Dutch scoundrel! Where is the boy I gave into your charge?" "Gone, Mr. Hook! Disappeared unter mein very nose. I take not mein eyes from him, und I looks for him und he ish not dere. I tink dere's some devil vork mit dis, by shiminy, I do!" A moment later, and Detective Hook, with the frightened German by his side, stood beneath the high wall skirting Trinity church-yard on the New Church street side, at the spot where Frank Mansfield had so strangely disappeared. Twice over had the wretched Schneider told his tale, without rendering matters in the least more clear. If he told the truth--and he related the facts so circumstantially that there could be no doubt of that--there was absolutely no explanation to be had. There was the dead wall upon one side broken only by the iron doors, leading to the vaults beneath the bank, which had not been opened, perhaps in a century, filled with the moldering bones of the long-forgotten dead, and the structure of the elevated railroad upon the other, with the dark outlines of the building upon the opposite side of the street rising just beyond. That the boy could have crossed the street was a simple impossibility. Not a trace of human foot was visible in the freshly fallen snow. Upon the sidewalk beneath the wall the detective had no difficulty in tracing his footsteps. But this only served to double the mystery. They all pointed one way--in the direction of the station toward which they had been going, and at the precise point where the boy had halted when the attention of his conductor had been attracted by the bat-like cry from the wall above they ceased to appear at all. It was impossible that the vanished prisoner could have advanced or retreated, crossed the street--moved up or down. Deeply puzzled, the detective hurried to Rector street again, and leaped the iron fence at the first available point, landing among the stones of the grave-yard beyond. Nor did he leave it until an hour had passed, and but little the wiser then. The tracks of two men crossing toward the Rector street side of the grave-yard from a point overlooking the place where Frank had disappeared were found and carefully measured. At this point, also, the snow was found to be much disturbed, both on the ground itself and upon the vines overhanging the wall.