“Certainly. Go as far as you like.”

Nick then began a careful inspection of the three back windows, all of which were found to be securely locked. None bore any evidence of having been recently opened. The floor near them bore no trace of earth, or dirt, denoting the recent presence of intruders.

So far as could be seen, in fact, even by the keen-eyed detective, everything in the rooms of Mr. Victor Gilbert was, as he had stated, precisely as he had left it.

“Is there a way to the roof?” Nick inquired, glancing up at a slightly sloping, twelve-foot skylight nearly in the middle of the ceiling.

“Yes. There is a ladder and a scuttle in my dark room,” said the photographer.

“Let’s go up there,” Nick said shortly. “I see that the roof is a flat one, or nearly so, and I wish to cover all of the ground.”

Mr. Gilbert again led the way.

One after another they mounted the ladder and crawled through the narrow scuttle. A stretch of slightly sloping, tar-and-pebble roof, the huge skylight aglow with light from below, the two chimneys with which the house was provided, the lower roof of that adjoining it, the gloomy side wall of the lofty Carroll Building, the black intervening abyss, the glare from the brightly lighted streets in other directions—only these and the purple dome of the starry sky met their searching gaze.

A fierce gust of wind caused the photographer to retreat toward the scuttle.

“By gracious, Carter, I’d rather venture up here by daylight, and in calm weather,” he shouted. “Go as far as you like, you two, but I am ducking back on the ladder.”