One Lost Summer by Richard Godwin

Rex Allen loves star quality in women. He moves into a new house in a heat wave with few possessions apart from two photographs of his dead daughter. His next door neighbour, beautiful Evangeline Glass invites him over to one of her many summer parties, where he meets her friends and possessive husband Harry. Rex feels he knows Evangeline intimately. He starts to spy on her and becomes convinced she is someone other than who she pretends to be. When he discovers she has a lover, he blackmails her into playing a game of identity that ends in disaster.