"What makes you think I did it?" asked Jack. "I was laid up with a
sprained ankle."

"That's just how I know it was you and some of your chums," cried
Professor Grimm. "Tied on the bell, where it had been used, so the
sharp edge would not cut one's fingers, was this rag. There it is.
Smell of it. What does it smell like?" and he thrust it under Jack's
nose.

"Why--why--it smells like arnica," replied our hero, wondering what
was coming next.

"Arnica! Yes, I guess it does. What was it you were pretending to put
on your ankle last night, Ranger? Arnica, wasn't it? Of course it
was. I've caught you this time! The evidence is all against you! You
didn't think you dropped that rag, and that the arnica would figure
in the evidence. Dr. Grimm, I repeat, Ranger must leave or I shall!"




CHAPTER III

A THREATENING LETTER


For a few seconds there was a silence following Professor Grimm's
ultimatum. Jack was so surprised he did not know what reply to make.
The suddenness of the accusation, with the experience of the night
before, and the upset over his sprained ankle, combined to make him