“Then I tell you what let’s do, dad.  Let’s drop everything in the inventive line and go off on a vacation.  I’ll take you up the lake in my boat and you can spend a week at the Lakeview Hotel at Sandport.  It will do you good.”

“What will you do, Tom?”

“Oh, Ned Newton and I will cruise about and we’ll take you along any time you want to go.  We’re going to camp out nights or sleep in the boat if it rains.  I’ve ordered a canopy with side curtains.  Ned and I don’t care for the hotel life in the summer.  Will you go?”

Mr. Swift considered a moment.  He did need a rest, for he had been working hard and his brain was weary with thinking of many problems.  His son’s program sounded very attractive.

“I think I will accept,” said the inventor with a smile.  “When can you start, Tom?”

“In about four days.  Ned Newton, will get his vacation then and I’ll have the canopy on.  I’ll start to work at it to-morrow.  Then we’ll go on a trip.”

Sandport was a summer resort at the extreme southern end of Lake Carlopa, and Mr. Swift at once wrote to the Lakeview Hotel there to engage a room for himself.  In the meanwhile Tom began to put the canopy on his boat and arrange for the trip, which would take nearly a whole day.  Ned Newton was delighted with the prospect of a camping tour and helped Tom to get ready.  They took a small tent and plenty of supplies, with some food.  They did not need to carry many rations, as the shores of the lake were lined with towns and villages where food could be procured.

Finally all was ready for the trip and the night before the start Ned Newton stayed at Tom’s house so as to be in readiness for going off early in the morning.  The day was all that could be desired, Tom noted, as he and his chum hurried down to the dock before breakfast to put their blankets in the boat.  As the young inventor entered the craft he uttered an exclamation.

“What’s the matter?” asked Ned.

“I was sure I locked the sliding door of that forward compartment,” was the reply.  “Now it’s open.”  He looked inside the space occupied by the gasoline tank and cried out:  “One of the braces is gone!  There’s been some one at my boat in the night and they tried to damage her.”

“Much harm done?” asked Ned anxiously.

“No, none at all, to speak of,” replied Tom.  “I can easily put a new block under the tank.  In fact, I don’t really need all I have.  But why should any one take one out, and who did it?  That’s what I want to know.”

The two lads looked carefully about the dock and boat for a sign of the missing block or any clews that might show who had been tampering with the arrow, but they could find nothing.

“Maybe the block fell out,” suggested Ned.

“It couldn’t,” replied Tom.  “It was one of the new ones I put in myself and it was nailed fast.  You can see where it’s been pried loose.  I can’t, understand it,” and Tom thought rapidly of several mysterious occurrences of late in which the strange man at the auction and the person he had surprised one night in the boathouse had a part.