“Humph,” grunted Mollie, getting to her feet rather unsteadily and shaking out her sodden skirts.  “I guess this isn’t the first time I have taken a dip in cold water.  And besides,” she added impatiently; “I don’t know about you girls, but I would like to know just what that thing was that we saw dart beneath the falls.”

“That was what made you fall into the water, wasn’t it?” asked Betty, her forehead wrinkling thoughtfully.  “You leaned so far out to see——­”

“Yes, yes,” Mollie interrupted impatiently, all her curiosity revived.  “That was what made me fall into the water all right.  But what I want to know is—­ what was it?”

“I don’t know,” said Betty, shaking her head.  “I didn’t see it.”

“Neither did I,” Grace added.

Mollie looked from one to the other of them open-mouthed.  Then she turned to Amy,

“You saw it, didn’t you?” she asked.  “You screamed, you know.”

“Yes,” said Amy, nodding her head very solemnly, “And it looked to me a lot like what we saw last night.”

“Thank goodness, you saw it too or the girls would surely think I had been dreaming or was crazy,” said Mollie, with relief.  Then she suddenly turned and started off into the woods.  “I’m going all alone to find out what that was,” she told her stupefied chums.  “I’ve got to clear up the mystery before I’m an hour older.”

But this time Mollie found that there was some one stronger than she, and that was Betty.  The Little Captain ran after her and brought her back, protesting but captive.

“We are going back to the house now and get you something hot to eat,” said Betty, as they rejoined Amy and Grace and started off toward home.  “Afterwards if everybody’s willing we will hunt this strange beast that jumps out from porches and leaps into rivers just for the fun of the thing.  But just now, Billy Billette, you are going home.”

But Mollie had been more severely shocked than she was willing to admit by her experience, and it was some time before the girls visited the falls or the river again.  Meanwhile they contented themselves with exploring the country about the lodge, taking short trips in the cars and wondering whether the boys would really be home before the summer was over.

Their days were not altogether happy, however, for the thought of that weird thing prowling around in the woods and ready, for all they knew, to spring out at them at every turn, refused to be banished from their minds.

Then, too, they thought a great deal about poor Professor Dempsey and the little ruined cottage in the woods.  Somehow, they had an uneasy feeling that if they had gone to him at the very first minute they had heard of his trouble they might have helped him.  Whereas, they had waited and—­ he had fled.

For a while the idea of a dip in the swimming pool was naturally not very attractive to Mollie, but at last there came a day when she herself suggested it and the girls enthusiastically seconded the motion.