"But what right have you to keep me here?" demanded the youth. "Who are
you, and what have I done to you, that you should treat me this way?
Are you crazy? Don't you know that you are liable to arrest for this?"

"No one can arrest me," boasted the fellow.

"But why have you made me a prisoner?" demanded Mark.

"For reasons of my own. You'll see very soon."

"But what have I done to you?" persisted the lad. "I never saw you
before, that I know of, unless you are the man who sent me the note,
and who ran when my chum and I came to the bridge to meet you."

"I'm the man," was the answer, with a chuckle.

"Then you must be the one who tried to wreck our projectile," went on
Mark.

"Yes, I did that, and now I am sorry for it, for I have thought of a
much better scheme for getting even, and having my revenge on you."

"But why do you want to be revenged on us?"

"Because of what you have done!" and the man's voice took on an ugly
tone.

"But what did we do?" begged Mark.