ll hereafter designate Tom's motor-boat) walked down toward
the dock where it was moored the young inventor gave a startled cry.

"What's the matter?" asked Mr. Hastings.

"That man! See him at my motor-boat?" cried Tom. He pointed to the
craft in the lake. A man was in the cockpit and seemed to be doing
something to the forward bulkhead, which closed off the compartment
holding the gasoline tank.

"Who is he?" asked Mr. Hastings, while Tom started on a run toward the
boat.

"I don't know. Some man who bid on the boat at the auction, but who
didn't go high enough," answered the lad. As he neared the craft the
man sprang out, ran along the lakeshore for a short distance and then
disappeared amid the bushes which bordered the estate of Mr. Hastings.
Tom hurriedly entered the ARROW.

"Did he do any damage?" asked Mr. Hastings.

"I guess he didn't have time," responded Tom. "But he was tampering
with the lock on the door of the forward compartment. What's in there?"

"Nothing but the gasoline tank. I keep the bulkhead sliding door
locked on general principles. I can't imagine what the fellow would
want to open it for. There's nothing of value in there. Perhaps he
isn't right in his head. Was he a tramp?"

"No, he was well dressed but he seemed very nervous during the auction,
as if he was disappointed not to have secured the boat. Yet what could
he want in that compartment? Have you the key to the lock, Mr.
Hastings?"

"Yes, it belongs to you now, Mr. Swift," and the former owner handed it
to Tom, who quickly unlocked the compartment. He slid back the door
and peered within, but all he saw was the big galvanized tank.

"Nothing in there he could want," commented the former owner of the
craft.

"No," agreed Tom in a low voice. "I don't see what he wanted to open
the door for." But the time was to come, and not far off, when Tom was
to discover quite a mystery connected with the forward compartment of
his boat, and the solution of it was fated to bring him into no little
danger.

"It certainly is odd," went on Mr. Hastings when, after Tom had secured
the screw driver from his motor-cycle tool bag, he aided the lad in
removing the letters from the bow of the boat "Are you sure you don't
know the man?"

"No, I never saw him before. At first I thought his voice sounded like
one of the members of the Happy Harry gang, but when I looked squarely
at him I could not see a bit of resemblance. Besides,