Undertow

"Carmen is happily married to Tom, although she knows she'll always live in the shadow of another woman--the mistress who ended his first marriage: Zena. Mercurial, mesmerizing, manipulative Zena--a woman who, Carmen begins to discover, had the potential to incite the darkest of emotions. Zena, who drowned in the sea late one night. Zena seems ever-more present, even in death, and when Carmen unknowingly stumbles on evidence that her husband has not been telling her the whole truth, she can't shake her unease"--Amazon.com.