Two fleeing figures scramble up the lonely hillside and disappear from Kay's view behind a rock ledge. Breathless, she climbs after them, determined to question them about the strange happenings at Owl's Hole, a summer resort. Suddenly a boulder comes crashing down the slope directly at Kay. She dodges quickly, the massive rock missing her by inches. By the time she has recovered and reached the ledge, the fugitives have accomplished a getaway!

But Kay is far from discouraged. She has been asked to solve the mystery of the summer resort, and is determined to do it. Mysterious fires have broken out. Valuables have vanished. Weird voices groan after dark, and stealthy shapes follow unwary strollers.

For a while, Kay's only clue is a single footprint. Whose is it, and why is he plaguing the innocent residents of Owl's Hole? Kay's clever detective work, with the aid of her two friends, Betty and Wilma Worth, carries her through one dangerous adventure after another. Jealous Ethel Eaton adds to the dilemma, nearly spoiling a perfect trap. Kay's search for the phantom troublemaker takes her to an unexpected solution, one that involves a missing member of her own family!