Dave,
warmly. "You'll remember the letter Mr. Sparr got, stating we were
guilty of trying to blow up his hotel. We are now satisfied that Mr.
Haskers penned that letter--in fact, we have the evidence to prove
it."

"Impossible!"

"No, sir, it is true, and I dare him to deny it. It is an absolute
fact, Doctor Clay, and we have come here this morning to inform you
that we can no longer attend a school where he is a teacher," went on
Dave, firmly.

"But--but you--er--you astound me, Porter! Tell me what you know, or
think you know."

In a plain, straightforward manner Dave mentioned the letter and the
printing that had appeared on it. Then he told how he and his chums
had searched the bedroom after the tree-top crash and found the
sheets of paper with that same printing, and he produced them.

"And we also found these, in a corner of the broken writing-desk," he
continued. "Some writing by Mr. Haskers, in which he practiced
backhand. This writing is just like that which appears in the letter
Mr. Sparr got. Compare the two and you will see we are right. Wilbur
Poole said Mr. Haskers saw him blow up the hotel, and he told the
truth, even if he is weak-minded."

"But why should Mr. Haskers do such an outrageous thing?" asked the
master of Oak Hall.

"I will tell you why, sir," returned Dave, and related the affair of
the Widow Breen. "That made him very sore on us, and he wanted to get
us out of the school. At first he tried it by overworking us in our
lessons, and when he found that that didn't work he tried this game of
making out that we were criminals."

"Yes, but--but would a teacher of mine stoop so low?" murmured the
worthy doctor, shaking his head doubtfully.

"No ordinary teacher would, Dr. Clay. But Mr. Haskers is not an
ordinary man--he is very dictatorial and harsh, and he hates boys even
though he has to teach them. He isn't a bit like Mr. Dale, or the
others."

"We never had any trouble with any teacher but Haskers," put in
Phil.

"And if we have to leave Oak Hall I'm going to get my father to sue
Haskers for damages," added Roger.

A talk lasting the best part of an hour followed, and at last the
worthy doctor had his eyes opened to the unworthiness of his
assistant. He scanned the sheets of paper and the writing the boys had
brought with interest.

"You are right--this is Mr. Haskers's hand," he said, slowly. "But is
it the same hand that wrote that villainous letter to Mr. Sparr?"

"Comp