The Lake House by James Patterson

Frannie O'Neill's life turned upside down when she and FBI maverick Kit Brennan rescued six incredible winged children from the school that created them. Now the young flock wants to go back to the couple, and Frannie and Kit are suing for custody. But when the case involves the most extraordinary creatures ever to land on this earth, someone will ensure there is no happy ending. Only Max, the most remarkable of the children, knows that another, terrifying biological experiment is taking place in the labs of a brilliant but evil surgeon, Dr Ethan Kane. But to complete his experiment he needs the ultimate prize - Max herself. And as the children dream of returning to the happy safety of the lake house, where for a few precious months they flew free, Kane moves ever closer...