When Maggie and Piper meet as girls on the Nantucket beach, they are instant best friends - even though Piper's mother would much prefer she play with the daughters of senators and statesmen than a seamstress's kid like Maggie. But after many golden summers spent building sandcastles and sharing their dreams for the future, Piper and Maggie grow apart. In her twenties, beautiful and spirited Piper worries she'll never amount to more than the glittering wife of a successful husband, while hardworking redheaded Maggie scrimps and saves her pennies, wondering if she'll ever have the luxury of a passionate romance. It seems they have little in common...until Cameron Chadwick appears on the island. A wealthy Midwestern charmer, Cameron takes moonlit walks on the dunes with Maggie and whisks Piper away to New York City for lavish nights on the town. When both women discover they're pregnant, it looks like the end of their already-distant friendship. But as Maggie and Piper struggle to decide what their lives will be, they realize more than ever before how very much they need a friend.