There is something strange about Sentinel House. From the first night they moved in, Graham and his sister Matty sense they are not alone in the house. With his father busy designing a top-secret weapons system, Graham is told to let his suspicions lie. But when the weird phenomena begin -- the voices, the mysterious writing appearing on a foggy window -- Graham decides to investigate. When his father is charged with a crime he did not commit, Graham's life turns upside down and his close-knit family is threatening to tear apart. Will Graham's family and life ever be the same? And just who is living in the Sentinel House? Part ghost story, part story of a family struggling to stay together, Operating Codes invites readers to consider the operating codes that influence the society in which they live.