Fourteen-year-old Will Burrows lives in the suburbs of London, or at least he did up until a few months ago. That's when his archaeologist father suddenly disappears. When the police fail to turn up any clues, Will takes it upon himself to search for his father. With the help of his best pal, Chester, they discover a hidden tunnel behind a bookcase in the basement. Positive that this is where his father went, Will and Chester delve into the tunnel as well, unaware of the adventure -- and horrors -- they are about to experience. Will and Chester discover an underground city called the Colony, ruled by the harsh and unrelenting Styx. They also learn another surprising fact: Will actually comes from the Colony. His mother, Sarah, took him and escaped to the surface when Will was a baby, and so the Burrows are actually his foster family. After years apart and not even knowing he existed, Will reunites with his younger brother, Cal. Another shocker is the fact that his foster sister, Rebecca, is a Styx and was spying on him all these years.