o-o-oh!"

Duff Salter was himself again.

"Well, Salter," continued the heir-apparent of Kensington, "we laid our
heads together, and the mystery continued to deepen why Andrew Zane
infested the residence of his murdered father if he never revealed
himself to the woman he had loved. Not until the discovery that Agnes
Wilt had been ruined could we make that out."

They were both looking at each other intently as Duff Salter read the
last sentence.

"It then became plain to us," continued Calvin, "that Andrew Zane wanted
to abandon the woman he had seduced, as was perfectly natural. He
haunted and alarmed the house and kept informed on all its happenings,
but cut poor Agnes dead."

"The infamous scoundrel!" exclaimed Duff Salter, looking very dark and
serious.

"Now, Salter," continued Calvin, "we had a watch set on that ridge of
roofs every night, and another one at the old Zane house, front and
rear, and the apparition on the roof was so irregular that we could not
understand what occasions it took to come out until we observed that
whenever your servant was out of the neighborhood a whole night, the
roof-walker was sure to descend into Zane's trap."

"Jer-i-cho-ho-ho!"

"To-night, as we have made ourselves aware, your servant is not in
Kensington. We saw him off to Treaty Island. I am watching at this
window for the man on the roof. The moment he leaves the trap-door of the
tenant's house, it will be entered by officers at the waving of this
lamp at my window. One officer will proceed along the roof and station
himself on the Zane trap, closing that outlet. At the same time the Zane
house will be entered front and rear and searched. The time is due. It
is midnight. Come!"

Calvin pointed to a ladder that led from the corner of his study to the
roof, and Duff Salter nodded his head acquiescently.

They went up the ladder and thrust their heads into the soft night of
early summer.

There was starlight, but no moon.

The engine bell just ceased to toll as they looked forth on the
scattered suburb, and at points beheld the Delaware flowing darkly,
indicated by occasional lights of vessels reflected upward, and by the
very distant lamps on the Camden shore.

Most of the houses within the range of vision were small, patched, and
irregular, except where the black walls of the even blocks on some
principal streets strode through.

Scarcely a sound, except the tree frogs droning, disturbed the air, and
Kensi