Langford is an estate owned by Mr. and Mrs. Mainwaring, where they live with his sister Maria Mainwaring. They host a house party, attended by Lady Susan Vernon and her daughter Frederica, Sir James Martin, and Charles Smith, during which the widowed Lady Susan begins an affair with Mr. Mainwaring and seduces Sir James away from Maria Mainwaring, intending for him to marry Frederica instead. When Frederica sets herself against Sir James and Mrs. Mainwaring becomes suspicious of her husband's relationship, Lady Susan sends Frederica to school and leaves to visit her brother-in-law.