Like a cuckoo hatched in the nest of unsuspecting smaller birds, the girl claimed to be Kate Seton's long-lost sister monopolizes Kate's parents' attention and threatens the family's unity. Emma was stolen from her pram before Kate's birth. Now, 12 years later. Rosie turns up with an apologetic letter from the woman who's been Mom to her; conscience requires her to return Rosie/Emma to her rightful parents. Rosie's brash, flashy, profane, with a clever mind of her own. The Setons can't be sure she's really Emma; while they try to find out they are anxious and preoccupied, leaving Kate feeling neglected and Rosie exasperated. Initial efforts to solve the mystery fail; but meanwhile, in a tentatively blossoming friendship where similar needs lead to sympathy and mutual support, Kate and Rosie subtly realize that they wish to be sisters before they find out whether they really are. Like Alcock's other stories (The Haunting of Cassie Palmer, etc.), an engrossing page-turner distinguished by fine writing and characterization.