Marie Louise Egerton Castle was the daughter of Agnes Mary Frances Sweetman and Egerton Castle. They married in 1883 and co-authored many novels with her husband.
Her mother also wrote plays for children, as well as stories for magazines such as Temple Bar, Cornhill Magazine, and Macmillan. Egerton Castle M.A., F.S.A. (12 March 1858 – 16 September 1920) was an author, antiquarian, and swordsman, and an early practitioner of reconstructed historical fencing, frequently in collaboration with his colleague Captain Alfred Hutton. He was born in London into a wealthy family; his maternal grandfather was the publishing magnate and philanthropist Egerton Smith.
