L. Frank Baum 
Mary Louise and the Liberty Girls 

Set during WWI, 'Mary Louise and the Liberty Girls’ is the fourth book in the popular children’s series by 'Oz’ author L. Frank Baum. Mary Louise and her friends decide to form a group to help raise money for the war effort, calling themselves the Liberty Girls. When the group hears about anti-war sentiment being spread in the town, they task themselves with discovering whether it comes from a spy hidden in their midst. –