The Bluebird Books series captivated teenage girls in the 1910s and 1920s, starting with Mary Louise, penned by L. Frank Baum under his Edith Van Dyne pseudonym. While Baum crafted the first four novels, the series continued with contributions from other authors, all maintaining the same pseudonym. The stories explore the adventures of adolescent girl detectives, a theme Baum had previously touched on in The Daring Twins and Phoebe Daring. The title character, Mary Louise Burrows, is a remarkably mature fifteen-year-old who faces a shocking challenge her beloved grandfather is accused of treason against the United States. With the help of both old and new friends, she embarks on a quest to uncover the truth. Notably, the story features federal agent John OGorman and his daughter Josie, a young investigator trained by her father, who breaks the mold of traditional femininity long before Nancy Drew. (Summary adapted from Wikipedia)