A well-regarded writer of suspense for children provides another tightly plotted story. Their mother abruptly takes Megan and Sandy, at night and without explanation, to her father's lakeside cottage to stay while she goes to find a new job in a new town. This latest in a series of moves arouses the children's suspicion that there is a mystery--and possibly danger--surrounding them, but Grandpa tries to respect Mom's wish to explain herself when she returns. Meanwhile, the kids explore the lake, tentatively make friends with Ben (the rebellious son of too-busy parents), and build a treehouse on a nearby island. When strangers begin to appear, having apparently traced the family through the postmark on a letter Megan sent her best friend, it is obvious that they seek the children, who finally hear about their own past and the search for them by their father's family--a search that has put them in danger of kidnapping. There are two stories here: a thoughtful novel about identity, and a rather routine suspense story involving poorly drawn villains. The first is the more original; but the second, with a satisfying number of twists and surprises, will keep the pages quickly turning till the end.