When teenaged Barbara Conwyne learns that cousins who marry risk having children with mental or physical handicaps, she fears that she and her beloved cousin William will never marry. The cousins, born only weeks apart, to identical twin mothers, and fathers who were brothers, are biologically closer than first cousins and therefore, believes Barbara, at even greater risk. Despite obsessively loving only each other, Barbara's fear of this 'forbidden' love blights the first part of the cousins' lives. While Barbara remains in the family mansion in Mount Eden, William moves to New Plymouth to start a new life. Only after twenty cheerless years apart does fate give the cousins a second chance to at last live together, where they belong, in the derelict family mansion, in blissful happiness. Until, once again, fate intervenes.