with envy. The more I think of it, the
surer I am it is Ada. Ruth doesn't dislike any one actively enough to
exert herself."

"Ada Nansen?" repeated Bob. "Isn't she that girl we saw on the train and
who plumped herself down in my seat? I thought so--I remember you told
me. Well, from the sidelight I have on her character, I believe she is
the one at the bottom of this. That will explain, too, why you never
catch any one digging up the bottle--she knows exactly when you are busy
and when you are not."

"Bottle!" said Betty explosively, to Bob's amazement. "Oh, Bob! this
morning Miss Jessup was talking to us about association of ideas, and she
asked Ada what bee meant to her. We thought she'd say 'honey,' of course,
but she said 'bottle.' Doesn't that show--"

"I should say it did!" Bob's voice was eager. "She took it for the letter
'B' and bottle was in her mind. You may depend upon it, that girl is at
the back of all this fuss! Gee, when I've nothing else to do, I'm going
to study up on this association of ideas stuff."

"You don't need it--you can get at things without a bit of trouble,"
Betty assured him affectionately.

"How will you go about pinning down Ada?" Bob asked anxiously.

"I'll cut out Latin to-morrow afternoon when she has a study period,"
planned Betty. "She'll think Libbie is reciting, and she'll not think of
me at all, and I'll slip out and watch to see if she goes near the
bottle. But what can I do if she does prove to be the right one? She'll
tell Mrs. Eustice, and poor Libbie will be in a peck of trouble. I really
think Mrs. Eustice would send her home if she knew."

"And serve Libbie right for being such an idiot!" pronounced Bob
severely. "However, I think she has been pretty thoroughly punished
through fear. I only wish you'd told me this before, Betty, because I
know exactly how you can deal with Ada."

"You do? Oh, Bob, what should I ever do without you!" cried Betty,
forgetting that a few moments before she had berated him for his
insistence. "Tell me, quick."

"Well, a crowd of us fellows happened to be over in Edentown last Friday
night, and we saw Ada and Ruth at the movies," said Bob. "They didn't see
us, for we sat back. They were the only girls from Shadyside, and Tommy
and I decided they had sneaked out after dinner and walked all that
distance. Now threatening isn't a very nice performance, Betty, but
sometimes you have to meet like with like. I think, if when you see Ada
di