when they learned that he was trying to practically hypnotize Mrs. Stanhope into marrying him, so that he could get control of the fortune which the widow was holding in trust for Dora. They foiled the teacher's efforts to wed the lady, and in the end Josiah Crabtree had to leave Putnam Hall. Later still he was arrested for some of his misdeeds and given a short sentence in jail.

The Stanhope fortune, as a part of the money coming to the Stanhopes and the Lanings was called, had come to Mr. Stanhope in a peculiar way, and some outsiders claimed the treasure, which, at that time, was secreted in a spot among the West Indies called Treasure Isle. There was a lively chase to get there first, but the Rovers won out, and because of this their enemies were more bitter than ever.

The boys had finished their term at Putnam Hall and on their return home became students at Brill College, a fine institution of learning of the Middle West. At the same time Dora, Nellie, and Grace became pupils at Hope Seminary, located not many miles from Brill. At the college the Rovers made many friends, including Stanley Browne, already introduced, and Will, otherwise known as "Spud," Jackson, a lad who loved potatoes, and who also loved to tell big yarns.

A term at college had been followed by a trip down East, taken for a peculiar reason, and then, while on a visit home, the three lads had become the possessors of an up-to-date biplane, which they named the Dartaway. In the biplane, as related in the volume before this, called "The Rover Boys in the Air," our heroes made a somewhat spectacular trip from the farm to the college campus, much to the amazement of their fellow collegians and their instructors. Later they made a trip through the air to Hope Seminary, and at that time Dick was delighted to place upon Dora's finger a diamond engagement sing.

A short while later an alarming thing occurred. The boys were out in the Dartaway when they met Grace on the road and learned that Dora and Nellie had been abducted by Josiah Crabtree, Tad Sobber, and some of their other old enemies. They gave chase in the biplane, and, after several adventures, located the girls in a lonely mansion in the country, where they were prisoners, in charge of Sobber's aunt The boys at once went for the authorities, and, after something of a fight, the rascals were made prisoners, and the girls were rescued and taken back to the Seminary.

"You will appear against these scoundrels?" asked the sheriff, Jackson Fells, of the Rover boys, as they were about to leave the sheriff's office at Plankville.

"We'll appear all right enough," Tom had answered. "Why, Mr. Sheriff, you couldn't beat us away with a club!" And so it had been arranged that the Rover boys should appear in court against the evildoers whenever wanted. Then Crabtree, Sobber, and the others had been put under lock and key in the old-fashioned country jail; and there, for the time being, the matter had rested.

"I wish we could learn more about Crabtree's escape," remarked Tom, as he and his brothers entered the main building of the college.

"So do I," added Sam. "Can't we telephone over to Plankville, to Sheriff Fells?"

"More than likely the sheriff is out, hunting for Crabtree and the others," answered Dick. "But I'll tell you what we might do—if the weather stays good," he added, suddenly.

"Sail to Plankville in the Dartaway?" queried both of the others.

"Yes, if Doctor Wallington will give us permission."

"He ought to—since we are so much interested in this case," returned Tom.

"We'll find out, as soon as the morning session is over," said the eldest Rover boy; and then all hurried to their classes, for the final bell had ceased to ring.

It was hard work for the boys to keep their minds on their lessons. Dick, especially, was very serious, and for a good reason. Something was worrying him greatly—something of which Tom and Sam knew little. What it was we shall learn later.

The boys had a quarter of an hour after classes before going to lunch, and they immediately sought out Doctor Wallington, whom they found in his private office.

"Yes, it is too bad that that rascal Crabtree escaped," said the head of the college. "I can well imagine that you are worried—since he has caused you and your friends so much trouble in the past. Let us hope that the authorities will quickly recapture him."

"Have you had any further word, sir?" asked Dick.

"I had word at eleven o'clock, from the newspaper office. Up to that time he had not been located."

"We wish to ask a favor," went on Dick, and spoke about the proposed trip to Plankville.

"Very well, you may go, and in your biplane if you deem it safe," said the worthy doctor. Secretly he was quite proud of the students' success with the Dartaway, as it had advertised Brill College not a little.

"Possibly we won't be able to get back until to-morrow," said Tom. "We may be detained, or it may storm."

"Take your time on the trip. Only be careful that you have no accidents."

"We'll try to be careful," answered Dick, with a grim smile. "We don't want a tumble if we can help it."

"It is a grand sport," answered the head of the college. "Before long I expect to see aeroplanes in constant use."

"Wouldn't you like to go up with us some day, Doctor?" questioned Tom, slyly.

"Well—er—perhaps, Thomas. But not just yet. I wish—er—to see them more in general use first." And then the doctor bowed the students out.

The boys lost no time in preparing for the trip to Plankville. After a somewhat hasty lunch they put on their flying suits and then went down to where the Dartaway was housed, in one of the buildings attached to the gymnasium.

"Looks to be all right," remarked Dick, after an inspection of the flying machine, and while Sam and Tom were filling the gasoline tank and the oil distributor.

The engine was tried out for a minute, and found to be in perfect order. As usual, as soon as the explosions of the motor were heard, a crowd commenced to gather, to see the start of the flight.

"Wish you luck!" cried Stanley.

"Say, look out that you don't forget how to stop and sail to the North Pole!" sang out Spud Jackson.

"As if that could really occur!" murmured William Philander Tubbs, with a lofty look of, disdain.

"Sure it could happen," returned Spud, good-naturedly. "Why, I heard of an airman who went up once and forgot how to turn his machine down, and he went around and around in a circle for sixteen hours. And then he dropped ker-plunk right on top of a baker's wagon and smashed twenty-six pies—all because his gasoline gave out."

"Ridiculous!" murmured William Philander.

"Absolute fact, Tubbs," responded Spud, earnestly. "Come with me, some day, and I'll show you where the pies made a dent in the street when the flying machine struck 'em." And then a general laugh went up, and the dudish student stepped back in the crowd, out of sight.

"All aboard!" sang out Dick, as he hopped into the driver's seat and took hold of the wheel. "Start her up, somebody!"

Sam and Tom got aboard and willing hands grasped the propellers and gave each a twist. Bang! bang! bang! went the explosions, and soon the propellers were revolving swiftly, and then with a swoop the Dartaway ran over the campus on its wheels and suddenly arose in the air. A cheer went up, and the students threw up their caps. Then Dick swung around in a quarter circle and headed directly for Plankville.

It was an ideal day for flying, not too hot or too cold, and with very little breeze, and that of the "steady" kind, not likely to develop "holes"—the one great terror of all airmen.

"Wish we had the girls along," remarked Sam, when they were well on the way.

"Not for this trip, Sam," answered Dick, grimly. "We have got our work cut out for us."

"Why, what do you mean?"

"If old Crabtree hasn't been caught yet