The Wife Upstairs by Rachel Hawkins

Jane envies the riches of the residents of Thornfield Estates, where she is a dog walker for several families. When she meets widower Eddie Rochester, she and Eddie are instantly attracted to one another. Soon, she is moving into Eddie's home and developing friendships with the women in the neighborhood. Jane is glad to leave behind a life of growing up in foster homes and keeping secrets; in fact, Jane isn't even her real name. Eddie harbors secrets of his own--less than a year ago, his wife Bea and her best friend Blanche were presumed dead after a boat accident. Eddie had Bea declared dead, but she is still alive, being kept prisoner in the attic. The Wife Upstairs is a twisty, suspenseful tale similar to The Last Mrs. Parrish and The Wife Between Us.