For some time longer the boat shot along over the waves, towed by its invisible force.  The boys, with the exception of Tubby, began to get anxious.  The shores of the mainland were dim in the distance behind them, and Topsail Island itself only showed as a dark blue dot.

Suddenly the motion ceased.

“He’s free of the line!” shouted Hiram, inwardly much relieved to think they had got rid of what to him was an alarming situation.

“No, he’s not,” replied Tubby, bending over the line.  “He’s still fast to us.  The line’s as tight as a fiddle string.”

He was standing up as he spoke, and as the Flying Fish gave a sudden, crazy jerk forward, he was almost thrown overboard.  In fact, he would have toppled into the sea if Merritt had not bounded forward and grabbed the fleshy lad just as he was losing his balance.

“We’re off again!” exclaimed Hiram, as the Flying Fish once more began to move through the water.

But now the creature that had seized Tubby’s big hook started to move in circles.  Round and round the Flying Fish was towed in dizzy swings that made the heads of her young occupants swim.

“Start the engine on the reverse, and see if that will do any good,” said Tubby, bending anxiously over his line.

Merritt brought the reverse gear to “neutral,” and then started it up, gradually bringing back the lever governing the reversing wheel till the Flying Fish was going second speed astern, and finally at her full gait backward.

The tug thus exercised seemed to have no effect on the monster that had caught Tubby’s bait, however.  With the exception that the speed was diminished a trifle, the Flying Fish was still powerless to shake off her opponent.

Suddenly, and without the slightest warning, a huge, shiny, wet body shot out of the water almost directly in front of the amazed and startled boys, and settled back with a mighty splash that sent the spray flying in a salt-water shower bath over their heads.

“Whatever was it?” gasped Hiram in awed tones.

“A shark,” replied Merritt, “and a whopper, too.  What are we going to do, Tubby—­keep on or cut loose?”

“Just a little longer,” pleaded the other.  “He must be tiring by this time.  If we can only wear him out, we can tow him ashore and make a little money out of him.  You know shark skin is valuable.”

“I’d rather have a whole skin of my own,” quavered Hiram, who had been considerably alarmed by the momentary glimpse he had had of Tubby’s quarry.

“He’s off again!” shouted Merritt, as the sea tiger started straight ahead once more.

Suddenly the line slackened again.

“Look out!” Tubby had just time to shriek the warning before a mighty shock threw them all off their feet in a heap on the bottom of the boat.

“Zan-g-g-g!”

The line twanged and snapped under the sudden strain, and a great rush seaward showed the boys, as soon as they recovered their senses, that they had lost their shark.