“The arrow is gone!”

There was no doubt of it.  The craft was not at the dock.  Breaking into a run, Tom hastened to the boathouse.  The arrow was not in there, and a look across the lake showed only a few rowboats in sight.

“That’s mighty funny,” mused the youth.  “I wonder—­”

He paused suddenly in his thoughts.

“Maybe Garret took it out to try and see that it worked all right,” he said hopefully.  “He knows how to run a boat.  Maybe he wanted to see how the rudder behaved and is out in it now.  He got through dinner before I did.  But I should have thought he’d have said something to me if he was going out in it.”

This was the one weak point in Tom’s theory, and he felt it at once.

“I’ll see if Garret is in his shop,” he went on as he turned back toward the house.

The first person he met as he headed for the group of small structures where Mr. Swift’s inventive work was carried on was Garret Jackson, the engineer.

“I—­I thought you were out in my boat!” stammered Tom.

“Your boat!  Why would I be out in your boat?” and Mr. Jackson removed his pipe from his mouth and stared at the young inventor.

“Because it’s gone!”

“Gone!” repeated the engineer, and then Tom told him.  The two hurried down to the dock, but the addition of another pair of eyes was of no assistance in locating the arrow.  The trim little motor craft was nowhere to be seen.

“I can’t understand it,” said Tom helplessly.  “I wasn’t gone more than an hour at dinner, and yet—­”

“It doesn’t take long to steal a motor-boat,” commented the engineer.

“But I think I would have heard them start it,” went on the lad.  “Maybe it drifted off, though I’m sure I tied it securely.”

“No, there’s not much likelihood of that.  There’s no wind to-day and no currents in the lake.  But it could easily have been towed off by some one in a rowboat and then you would not have heard the motor start.”

“That’s so,” agreed the youth.  “That’s probably how they did it.  They sneaked up here in a rowboat and towed the arrow off.  I’m sure of it.”

“And I’ll wager I know who did it,” exclaimed Mr. Jackson energetically.

“Who?” demanded Tom quickly.

“Those men who were sneaking around—­Happy Harry and his gang.  They stole the boat once and they’d do it again.  Those men took your boat, Tom.”

The young inventor shook his head.

“No,” he answered, “I don’t believe they did.”

“Why not?”

“Well, because they wouldn’t dare come back here when they knew we’re on the lookout for them.  It would be too risky.”

“Oh, those fellows don’t care for risk,” was the opinion of Mr. Jackson.  “Take my word for it, they have your boat.  They have been keeping watch, and as soon as they saw the dock unprotected they sneaked up and stole the arrow.”