"My name is Mary Cary. I live in the Yorkburg Female Orphan Asylum. You may think nothing happens in an Orphan Asylum. It does. The orphans are sure enough children, and real much like the kind that have Mothers and Fathers; and that's why I am going to write this story." So begins Mary's diary, which she fills with her various doings and misadventures at the Asylum in Virginia and her sharp observations about life and human nature. She loathes Miss Bray, the head of the Asylum, who is not above telling bald-faced lies to the Board to further her own selfish ends. She loves Miss Katherine, the Asylum's resident nurse, who has befriended Mary and serves as a gentle role model for the child. As for Martha, she is Mary's "other self" who speaks out-and sometimes acts out-in spite of Mary's better nature. When she unexpectedly discovers her family background, Mary writes a letter to her uncle that leads to some surprising results on the way to a happy ending.

The Chicago Record-Herald of March 12, 1910 stated, "Let's be glad for books like Mary Cary. It isn't so much what Mary Cary does, however, as what she is, bless her! that warms the cockles of the chilliest, most snugly corseted heart." (Summary by Jan MacGillivray)