Weep for Me — John D. MacDonald

When Kyle Cameron meets temptation in the memorable shape of Emily, the strange, lovely new girl at the bank, his life changes forever. Emily has a fortune that frees him from his worst nightmares. But the relationship comes at a terrifying cost. Soon Kyle enters a world in which it will be impossible ever to feel safe again. He has placed his life in the hands of an insatiable woman with no fear of death . . . and no regard for anyone who stands in her way.