East Lynne by WOOD, Mrs. Henry

Ellen Wood (1814-1887) was an English novelist, better known as Mrs. Henry Wood. She wrote over 30 novels, many of which (especially East Lynne which was a Victorian best seller and is still sometimes performed as a drama) enjoyed remarkable popularity. Lady Isabel Carlyle, a beautiful and refined young woman, leaves her hard-working but neglectful lawyer-husband and her infant children to elope with an aristocratic suitor. After he deserts her, and she bears their illegitimate child, Lady Isabel disguises herself and takes the position of governess in the household of her husband and his new wife. Summary by Wikipedia