Billie Bradley and Her Classmates by Janet D. Wheeler

Billie and her chums come to the rescue of several little children who have broken through the ice. There is the mystery of a lost invention, and also the dreaded mystery of the locked school tower. (Summary from original advertisement)<br /><br /> <br /><br />This is the fourth book in the "Billie Bradley" series, a mystery series for girls. Janet D. Wheeler is a pen name used by the Stratemeyer Syndicate for the Billie Bradley series.