As children, Tam and her older brother were training to be Olympic swimming champions. Pitted in a practice race against each other, Tam was out in front, proving that she had the superior skills, until she suddenly suffered her first epileptic seizure. Just as he passed her to win, Tam's brother pulled her from the water, saving her life. He was dubbed a hero and his adult life continued with heroic exploits in canine search-and-rescue at earthquakes and terrorist bombings, but Tam, who steadfastly refused to enter the water again, never forgave her brother for finishing the race, while she'd felt she had no choice but to wear the mantle of ''disabled.''Thus started 30 years of careful vigilance to never again allow her body to betray her, nor her brother to ever again exert influence on her path. But eventually Tam finds that her life of cautious control and the arm's length estrangement that she's mentally maintained with her family has taken its toll. She's retired early, feels useless and in limbo, and makes an abrupt decision to visit Maine and assist in her sister's genealogy research by exploring a legend that suggests an ancestor was the sole survivor of a shipwreck - a baby girl rescued by a lighthouse-keeping great great grandfather.In Maine, Tam meets a distantly removed cousin, Nat, who tells her of another local legend, an unidentified woman who is said to have returned to the lighthouse in the 1930's to drown herself, and whose ghost is sometimes seen at twilight walking the rocky shore.Together they fabricate a fantasy version of their ancestors' experience in the remote lighthouse, where it's possible a shipwrecked baby did wash to shore, and irrevocably changed generations of lives-a fantasy that also has a sexual component for the two of them. Still retaining an adolescent vision of herself as a partial invalid, Tam has had a habit of living and reliving the minor traumas of her past-but Nat gives her the chance to be someone different, yet still the same: Tam is, for all intents and purposes, a ghost, but Nat's version of her ghostliness ascribes to it the kind of heroic mystery and romance that Tam has always assumed her brother to have but which Nat now gives her for herself.Meanwhile, in the real world, to add to the drama, Tam has ''rescued'' a baby who has been taken from his teenage mother, by sneaking it out from the small seaside hospital, and hiding both mother and child with herself at the privately owned lighthouse where her ancestors once lived.Tam's romantic quest to experience her ancestors' tragedies and heartbreak takes the particular form of a fascination with Mary Catherine, an ancestor who died at the age of 33 and onto whom Tam projects all her own anxities but this alternate life is invaded by the reappearance of her brother. And Tam, in a commanding re-entry into the water, chooses to close the book on her life of self-imposed susceptibility.