d whether he could have been deceived, but the
next he knew it was impossible. The light might have been fancy, or a
reflection, but there was none about that ladder.

Then his heart seemed to jump into his mouth, for there was a sound
overhead. Some one had evidently gone to the opening, stepped into the
little gallery, felt for the ladder, found it gone, and concluding that
the movable top had swung round, was now hurriedly spinning the wheel
and causing the whole of the light wooden dome to revolve.

"Caught," cried Tom beneath his breath; and, reckless of consequences,
he crossed the laboratory, ascended the steps, and dashed across to
where the iron wheel was pivoted to the wall.

"It's no good," he shouted. "Give up!" and he caught some one by the
shoulder; but before he could get a good grip he received a tremendous
buffet in the chest, which sent him staggering backward, and ere he
could recover himself his adversary had made for the trap-door, and
begun to descend as if quite at home in the place.

Tom made after him, but in the darkness he bore too much to his right,
and as he corrected his course by touch, he only bent down to descend in
time to feel the trap-door brush by him, and fall with a bang, which
forced from him a cry, mingled with the shooting of the bolt.

Fortunately as well as unfortunately, the trap-door fell upon Tom's
foot, which was half over the opening, and the bolt shot into vacancy,
so that the next minute the boy had dragged it up, descended two or
three steps, holding on by the edge of the floor, and then swung himself
forward and dropped into the chamber below.

"You stop, or it'll be the worse for you," he shouted fiercely, for the
pain in his foot had roused him into a fit of passion which drove away
everything but the desire to get a good grip of Pete.

There was no reply, no sound, and Tom felt that the scoundrel must be
close at hand stooping behind one of the tables or crouching against the
wall.

"It's of no use," cried Tom fiercely. "You're caught like a rat in a
cage. Do you hear, sir? Give in!"

_Creak_, _creak_! just as Tom was craning his head forward.

The sound came from below, and with a muttered ejaculation, full of
vexation, the boy darted to the head of the steps, and rushed down in
the darkness at a break-neck speed, which ended in a big jump on to the
stone-floor, from whence he rushed toward the window which made that
noise when any one tried to op