When they caught sight of each other’s faces they began to laugh shakily.

“We certainly look as if we were going on a ghost hunt,” Mollie said.  At this Grace uttered a little cry of protest.  The thought had struck too near her own disquieting thoughts to be comfortable.

“For goodness’ sake, somebody say something cheerful,” she begged.  “I’ve got to get up my courage some way.”

“Well, I haven’t any to lend you,” grumbled Mollie, as she linked her arm in Betty’s and the two went along toward the path.  “I don’t like this job a little bit.”

“Don’t you think,” suggested Amy, holding back a little, “that somebody ought to stay here and take care of the cars?”

“No, you don’t!” said Mollie, catching her by the hand and pulling her along after them.  “If one of us goes we are all going.”

“Oh, come along,” urged Betty, eager to get the thing over with.  “I think we are all acting like a lot of geese.  It might help some if we tried to remember that we are Outdoor Girls.”

This challenge did a great deal toward bolstering up the girls’ courage and they hurried along the path more confidently,

Their pace slowed a bit, however, when they reached the cleared space where the little cottage stood and they paused for a moment in the shelter of the trees to discuss what to do next.

“Do you think we had all better go?” asked Grace nervously.  “Perhaps the four of us would frighten him——­”

“No, we will all go together,” said Betty decidedly.  “There is nothing to be gained by standing here talking about it.  Come on, girls.”

She started across the cleared space and the girls followed slowly.  The little cottage looked deserted and forlorn and the dreary aspect of it served to increase the girls’ uneasy sense of disaster.

Betty knocked gently on the door which had, upon that other occasion not so very long ago, been hospitably opened to them.  But, though they waited breathlessly for a response, none came—­ the house was as silent as a tomb.

“Do it again, Betty.  He might be asleep or something,” suggested Mollie, with a glance over her shoulder at the quiet woodland.  “Knock harder this time.”

Betty obeyed, but with no better success than the first time.  Everything was as silent as before.

“Isn’t there a bell, I wonder?” suggested Amy, wishing ardently that they were back on the road once more.  “Perhaps your knock isn’t loud enough for him to hear.”

“We might tap on the window,” suggested Grace.  “If I use my ring on the window pane he surely ought to hear that.”

She started to suit her action to the words when an exclamation from Betty made her pause.  The latter had tried the door and found to her surprise that it gave to her touch.

“The door is unlocked,” she said.  “I don’t believe the professor is in here at all and if he has gone into the woods to hunt his butterflies and beetles I am sure he wouldn’t mind our going inside.  What do you think?”