ols, and Mr. Jackson, the engineer, was
temporarily away. Mrs. Baggert, in the house, could not hear his cries.

"I'm locked in!" cried Tom aloud. "The worm gear must have shut of
itself. But I don't see how that could be. I've got to get out mighty
soon, though, or I'll smother. This tank is airtight, and it won't take
me long to breath up all the oxygen there is here. I must get that
slide open."

He sought to grasp the steel plate that closed the emergency opening.
His fingers slipped over the smooth, polished surface. He was
hermetically sealed up--a captive! Blankly he set his lantern down and
leaned hopelessly against the wall of the tank.

"I've got to get out," he murmured.

As if in answer to him he heard a voice on the outside, crying:

"There, Tom Swift! I guess I've gotten even with you now! Maybe next
time you won't take a reward away from me, and lick me into the
bargain. I've got you shut up good and tight, and you'll stay there
until I get ready to let you out."

"Andy Foger!" gasped Tom. "Andy Foger sneaked in here and turned the
gear. But how did he get to this part of the coast? Andy Foger, you let
me out!" shouted the young inventor; and as Andy's mocking laugh came
to him faintly through the steel sides of the submarine, the imprisoned
lad beat desperately with his hands on the smooth sides of the tank,
vainly wondering how his enemy had discovered him.

Chapter Five

Mr. Berg is Suspicious

Not for long did the young inventor endeavor to break his way out of
the water-ballast tank by striking the heavy sides of it. Tom realized
that this was worse than useless. He listened intently, but could hear
nothing. Even the retreating footsteps of Andy Foger were inaudible.

"This certainly is a pickle!" exclaimed Tom aloud. "I can't understand
how he ever got here. He must have traced us after we went to Shopton
in the airship the last time. Then he sneaked in here. Probably he saw
me enter, but how could he know enough to work the worm gear and close
the door? Andy has had some experience with machinery, though, and one
of the vaults in the bank where his father is a director closed just
like this tank. That's very likely how he learned about it. But I've
got to do something else besides thinking of that sneak, Andy. I've got
to get out of here. Let's see if I can work the gear from inside."

Before he started, almost, Tom knew that it would be impossible. The
tank was made to clo