And then a wealthy Upper East Side woman pays her a visit. Amber Randall is concerned about her twin sixteen-year-olds, Lark and Fox, who have acted and looked very different since they returned from spending the summer with their British father in the UK. She tells Jessica that her children have unnaturally perfect skin for teenagers and have lost all the tics and habits that made them who they were. They are not Lark and Fox, she tells Jessica. Something has happened to them. To find out more, Jessica travels to Essex to talk to their father and once there meets Belle who is living a curiously isolated existence in a run-down farmhouse with her guardian Debra. Jessica knows that Lark and Fox had spent the summer with Belle—but can this unworldly teenager really be responsible for Lark and Fox's new personas? Jessica soon discovers that, behind Belle and Debra, evil geniuses are playing a dangerous game with technology in order to make the world a "better place", not caring who gets hurt, maimed or even killed in the process. Can Jessica stop them from wreaking destruction on a whole generation of young people?