Most of Clapp's novels were written as fictionalized accounts of historical events. "Dr. Elizabeth: The Story of the First Woman Doctor" (1974) focuses on the life of Elizabeth Blackwell who was the first woman to receive a medical degree in the United States. "I'm Deborah Sampson: A Soldier in the War of the Revolution" is loosely based on the life of Deborah Sampson, a young woman who disguised herself as a man and served in the 4th Massachusetts Regiment during the Revolutionary War. "Witches' Children: A Story of Salem" (1982) and "The Tamarack Tree: A Novel of the Siege of Vicksburg" (1986) explore the history of the Salem witch trials and the Siege of Vicksburg during the Civil War, respectively.