-"

Then Nort stopped, for he realized that, though he might apply some
well-deserved slang names to the two professors, neither of them was
"big." They were small men--at least in stature.

"But you haven't any right to hold us here prisoners!" declared Dick,
feeling that he must back up his brother in a firm protest. "We
haven't done anything to you."

"Except to turn up where you aren't wanted!" broke in Silas Thorp. "If
you'd minded your own business, and stayed away--let us alone--we
wouldn't have to do this!"

In surprise at such a statement, Nort and Dick looked at the two
professors.

Mr. Wright, with a wave of his hand toward his helper, to enjoin
silence, made this statement:

"Mr. Thorp has put the matter rather crudely, perhaps, but that is the
state of the case. Without going into details, boys, we are in this
part of the country on a secret mission. We have almost accomplished
what we are after, and, on the verge of the discovery, we do not wish
to be balked. You happen to have stumbled upon us just when we are
about to complete a wearisome search, which at least promises to be
successful.

"We have enemies who would be glad to frustrate our schemes, and it is
to prevent these enemies from obtaining knowledge of our movements, of
our location, and the location of that which we are seeking, that we
are forced to detain you. We hope soon to end our mission, and, once
we have gained possession of what we are after, we shall be most happy
to restore you to liberty."

He took breath after this somewhat lengthy address, and Nort and Dick
looked at one another, more puzzled than before. What did it all mean?
What was the queer secret of the professors, a secret that, somehow,
seemed to involve Diamond X?

"Do you mean that you're keeping us here because you're afraid we'll
tell something about you?" burst out Nort.

"Yes," answered Professor Blair. "We simply must keep our secret safe,
now that we are on the verge of discovery."

"But we wouldn't tell!" declared Nort. "In fact we don't know anything
about you--except that we've seen you once or twice. We don't know
what your secret is--that is, we can only _guess_ at it."

"That's just it!" interrupted Professor Wright. "You are the sort of
lads who would make a correct guess, and then, when word of it got out,
we would lose the fruits of many weary years of research."

"But we wouldn't tell anyone!" promised Dick. "All we know about