First Summer Love — Stephanie Foster

Lynn Madison is sure her summer vacation is ruined when she discovers that her family and the noisy, disorganized Cassidy's have accidentally rented the same beach house. Rather than argue, Lynn's father agrees to share the house for a month. But Lynn doesn't like the Cassidy's, and Jody Wilson, Mrs. Cassidy's "mother's helper", is the most irritating boy Lynn's ever met.

Lynn's feelings about Jody begin to change, but she's sure he has lots of girlfriends at home. To get him interested, Lynn invents a boyfriend of her own - only to find herself caught in a lie that might turn Jody off for good.