Click! click! click! went three pairs of skates as three snugly-dressed girls fairly flew along the frozen surface of the lake."Isn't it glorious?" cried the laughing, brown-eyed one, who was no other than Billie Bradley, as she threw back her head and sniffed the crisp, cold air. "Who ever heard of the lake freezing over in the middle of November? And the ice is pretty solid, too.""In spots," added Violet Farrington, a slender, dark girl with black hair and dark eyes."What do you mean-'in spots'?" asked the third of the trio, Laura Jordon. Laura was as fair as Violet was dark, and now her blue eyes darted an anxious glance at her chum. "Do you think we shall find any thin ice?""I don't know, of course," Violet answered quickly. "But you notice Miss Walters told us to stay close to the shore, and that certainly looks as if she weren't any too certain about the ice."Miss Walters was the much-loved principal of Three Towers Hall, the boarding school which the girls were attending, and to the three chums, Miss Walters' word was law.