(from: Wilkie Collins: An Illustrated Guide © Andrew Gasson 1998, used with permission)
After a traumatic childhood and youth, Sydney Westerfield is rescued from the drudgery of teaching in her aunt's school by becoming the governess of Kitty, only child of Herbert and Catherine Linley. Herbert and Sydney fall in love and matters are brought to a crisis by the meddling of Mrs Presty, Catherine Linley's mother. Sydney leaves the household but is brought back when Kitty becomes seriously ill, pining for her beloved governess. The situation deteriorates further and Catherine leaves her husband. To avoid custody of the child being given to Herbert, she goes into hiding with her mother and Kitty, obtaining a divorce under Scottish law. Kitty, however, is miserable. She misses her father and her governess--she is told her father is dead--and lacks companions because other children are not allowed to play with the child of divorced parents.
Matters are further complicated by the introduction of a friend of Sydney's dead father, Captain Bennydeck, who is searching for her. He falls in love with Catherine but withdraws a proposal of marriage when he learns she is divorced. A somewhat contrived happy ending is brought about when Sydney, tormented by her guilty conscience, leaves Herbert and the Linleys are reunited by Kitty and remarry. Sydney becomes Captain Bennydeck's secretary and the reader is left with the expectation that they will marry.