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.
To all appearance, a number of persons had been moving about here, but their foot-prints seemed to lead nowhere, extending simply up and down the wall.
What did it mean?
Detective Hook had been called upon to solve many mysteries in his time, but never before had he encountered one so deep as this.