se could obtain access to the
roof of the back building, he would be able to walk across that of the
first or adjoining house, and reach a point directly beneath where he
stood.

But, granting the possibility of this, of what use would it be? A person
on the roof below him would in no conceivable way be able to reach
either of the windows of Ruth Morton's room. Was it possible that an
opening had been made through the wall of the apartment building itself?
He thought it unlikely, but determined to investigate.

"I must get down on that roof below," he informed his companion. The
janitor grinned.

"How are you going to do it?" he asked.

"Haven't you a ladder--a rope?"

The man thought a moment.

"I've got a short ladder in the cellar, only about eight feet long, I
guess. I'm afraid it would not do."

"Yes it would," replied Duvall, pointing to the roof of the attic
portion of the house below. "I'll get down to the roof of the main part
of the house first, and from there to the roof of the back building. An
eight-foot ladder will be long enough for that. Bring it up, will you?"

The man hesitated.

"I don't just like this idea of going on other people's roofs," he said.

"You don't need to go. I've got to. I'm a detective, and I'm working for
Mrs. Morton on a most important case." As he spoke, he took a bill from
his pocket and pressed it into the man's hand.

The janitor responded at once.

"I'll fetch it up, sir," he said. "Wait for me here."

Duvall occupied the few moments consumed by the janitor's absence in
examining, by means of his pocket electric torch, the surface of the
roof on which he stood. The smooth flat terra cotta tiles showed no
distinguishing marks. Here and there spots of paint, marred by
footprints, indicated where the painters at work on the building had set
their buckets, no doubt while painting the wooden portions of the
trapdoor, and the metal chimney-pots on the roof.

The man returned in a few moments with the ladder, and Duvall, lowering
it to the level of the main portion of the adjoining house, saw that it
was of sufficient length to permit his descent. In a moment he had
slipped off his shoes, and was cautiously descending the ladder.

Once on the surface of the main roof of the house, he had intended to
take down the ladder and, by means of it, descend the remaining six or
seven feet to the roof of the back building, but he found that means for
this descent already exis