“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, that gang would not venture again into this neighborhood.”

“No, I imagine not.  Perhaps he was only a curious, meddlesome person.  I have frequently been bothered by such individuals.  They want to see all the working parts of an automobile or motor-boat, and they don’t care what damage they do by investigating.”

Tom did not reply, but he was pretty certain that the man in question had more of an object than mere curiosity in tampering with the boat.  However, he could discover no solution just then, and he proceeded with the work of taking off the letters.

“What are you going to do with your boat, now that you have it?” asked Mr. Hastings.  “Can you run it down to your dock in the condition in which it is now?”

“No, I shall have to go back home, get some tools and fix up the motor.  It will take half a day, at least.  I will come back this afternoon and, have the boat at my house by night.  That is if I may leave it at your dock here.”

“Certainly, as long as you like.”

The young inventor had many things to think about as he rode toward home, and though he was somewhat puzzled over the actions of the stranger, he forgot about that in anticipating the pleasure he would have when the motor-boat was in running order.

“I’ll take dad off on a cruise about the lake,” he decided.  “He needs a rest, for he’s been working hard and worrying over the theft of the turbine motor model.  I’ll take Ned Newton for some rides, too, and he can bring his camera along and get a lot of pictures.  Oh, I’ll have some jolly sport this summer!”

Tom was riding swiftly along a quiet country road and was approaching a steep hill, which he could not see until he was close to it, owing to a sharp turn.