had shut off the gasoline cock leading from the tank of his boat to the motor. It was a calm, early summer night, with a new moon giving a little light, and the lad went down to the lake in his slippers. As he neared the boathouse he heard a noise.
"Water rat," he murmured, "or maybe muskrats. I must set some traps."
As Tom entered the boathouse he started back in alarm, for a bright light flashed up, almost in his eyes.
"Who's here?" he cried, and at that moment some one sprang out of his motor-boat, scrambled into a rowing craft which the youth could dimly make out in front of the dock and began to pull away quickly.
"Hold on there!" cried the young inventor. "Who are you? What do you want? Come back here!"
The person in the boat returned no answer. With his heart doing beats over-time Tom lighted a lantern and made a hasty examination of the Arrow. It did not appear to have been harmed, but a glance showed that the door of the gasoline compartment had been unlocked and was open. Tom jumped down into his craft.
"Some one has been at that compartment again!" he murmured. "I wonder if it was the
