Mignon is the daughter of a young couple who are secretly and unhappily married. The father is an unlikable officer in an English regiment, the Scarlet Lancers, The mother of the child, desiring to keep her vow regarding the secrecy of her marriage, but unable to support her baby, decides to leave it in the father's rooms and force him to provide for it. By mistake she enters the wrong door and leaves the child in the room of 'Bootles', a popular member of the company...
Grace Harcourt leaves her baby at the army barracks after she has been jilted by its father, and her secret husband, the despicable Captain Gilchrist. The baby, named Mignon, is raised by Captain Ferrers (familiarly known as Bootles) with the help of the motherly Mrs Simmons, who has thirteen children of her own.
In the second act, set some five years later, Ferrers falls in love with Grace, who is now the companion to Lady Deveraux. Gilchrist meanwhile has begun to court Lady Devereaux. Grace exposes her ex-husband, and shortly afterwards, in the third act (set in a room overlooking the Blanktown racecourse), Gilchrist is thrown from his horse while riding in a hurdle race. With Grace now free to marry Ferrers, the baby's identity is finally made known.
