Beneath the Crimson Brier Bush — Frances K. Judd

The weird cry outside sounds almost human . . . Kay Tracey follows the faint cries to a thicket, and bends down to pick up a tiny bundle half-hidden beneath the leaves. As she draws aside a soft blanket, a tiny baby girl opens her eyes, whimpering as she nestles in Kay's arms.

Whose baby is this, and why has she been abandoned at the lonely farm? Kay's efforts to find the answer are made infinitely more difficult by another perplexing problem. Ethel Eaton, her jealous rival at Carmont High School, has disappeared. Mrs. Eaton, worried to distraction, appeals to Kay to help find her.

Kay discovers that Ethel has run away from home to become a detective herself. But this impulsive action leads Ethel into bad company -- a scheming couple trying to master-mind a blackmail plot! Kay's deductions and her efforts to save her rival get her in and out of many tight spots.