make sure there were no leaks in it. "To get even
with me for outbidding him on the boat, Andy may have wanted to destroy
the ARROW. Well, of all the mean tricks, that's about the limit! But
wait until I see him. I've got evidence against him," and Tom looked
at the key ring. "I could almost have him arrested for this."

Going outside the boathouse, Tom stood on the edge of the dock and
peered into the darkness. He could hear the faint sound of someone
rowing across the lake, but there was no light.

"He had one of those electric flash lanterns," decided Tom. "If I
hadn't found his keys, I might have thought it was Happy Harry instead
of Andy."

The young inventor went back into the house after carefully locking the
boat compartment and detaching from the engine an electrical device,
without which the motor in the ARROW could not be started.

"That will prevent them from running away with my boat, anyhow,"
decided Tom. "And I'll tell Garret Jackson to keep a sharp watch
to-night." Jackson was the engineer at Mr. Swift's workshop.

Tom told his father of the happening and Mr. Swift was properly
indignant. He wanted to go at once to see Mr. Foger and complain of
Andy's act, but Tom counseled waiting.

"I'll attend to Andy myself," said the young inventor. "He's getting
desperate, I guess, or he wouldn't try to set the place on fire. But
wait until I show him these keys."

Bright and early the next morning the owner of the motor-boat was down
to the dock inspecting it. The engineer, who had been on watch part of
the night, reported that there had been no disturbance, and Tom found
everything all right. "I wonder if I'd better go over and accuse Andy
now or wait until I see him and spring this evidence on him?" thought
our hero. Then he decided it would be better to wait. He took the
ARROW out after breakfast, his father going on a short spin with him.

"But I must go back now and work on my gyroscope invention," said Mr.
Swift when about two hours had been spent on the lake. "I am making
good progress with it."

"You need a vacation," decided Tom, "I'll be ready to take you and Ned
in about two weeks. He will have two weeks off then and, we'll have
some glorious times together."

That afternoon Tom put some new style spark plugs in the cylinders of
his motor and found that he had considerably increased the revolutions
of the engine, due to a better explosion being obtained. He also made
some m