ugh of course there was no certainty that they were
for that night. Upon this meagre hope he hastened up-town and stationed
himself where he could keep an eye on all who entered. At ten minutes
past eight he was about concluding that his task was useless when a cab
stopped, and to his intense satisfaction he saw Mr. Mitchel alight, and
then hand out a handsomely-dressed woman. Wilson had prepared himself
for this possibility, by purchasing a ticket of admission, so that he
followed the couple into the theatre, determined not to lose sight of
his man again. The opera over, he found it easy to shadow the two, as
the woman declined the proffered cab, perchance because the
exhilarating, though cold night air made a walk home inviting. He was,
however, somewhat amazed at last to see them enter the very
apartment-house on Thirtieth Street to which he had traced Rose Mitchel
in the morning. His mind was at once set at ease, for since both of his
birds had flown to the same dove-cot, it seemed plain that they were
connected. Evidently it was to this house that Mr. Mitchel had gone
after eluding him in the morning. At least so argued the astute
detective.

Wilson had waited opposite the building perhaps an hour, lulled into
abstraction of thought by the silence of the neighborhood, when he was
startled by hearing a piercing shriek, loud and long continued, which
then died away, and all was still again. Whether it came from the
apartment-house or one of the private dwellings next to it, he was in
doubt. That it was a woman's cry he felt sure. Was it a cry of pain, or
the shriek of nightmare? He could not tell. That solitary, awful cry,
disturbing the death-like stillness, seemed uncanny. It made him shiver
and draw his cloak closer about him. If it had only been repeated, after
he was on the alert, he would have felt better satisfied; but though he
listened intently he heard nothing. Ten minutes later, another thing
occurred, which attracted his attention. A light in a window on the
fifth floor was extinguished. There was certainly nothing suspicious
about this, for lights are usually put out when one retires. He noticed
it because it was the only light which showed from any of the windows
during his vigil. Whilst he was thinking of this, the door opposite
opened and a man emerged. Judging it to be Mr. Mitchel, he hastily
followed. That there might certainly be no mistake, Wilson walked
rapidly enough to reach the Avenue corner a