The Secret at the Windmill — Frances K. Judd

At the foot of the stairway Kay peers cautiously into the dark living room. She can see nothing but she feels a presence in the room. Suddenly her arms are pinned to her sides. Something soft and feathery is thrust against her face, smothering her.

The girl fights desperately. The robber must not escape with the money Kay has been guarding. In an instant she is released, the front door slams, and the intruder is gone!

How is Kay to recover the treasure entrusted to her? Who really owns it? The ragged old man in whose clothes it had been found? Or pretty Juliana Van Camp, whose wedding depends largely on solving the baffling mystery?

To add to Kay's difficulties, jealous Ethel Eaton tries her best to wreck both Juliana's happiness and Kay's reputation as a highly successful amateur detective. She nearly succeeds, but Kay and her friends, Betty and Wilma Worth, team up to solve a triple mystery in the shadow of a strange and forbidding windmill.