Tunnels by Roderick Gordon and Brian Williams and Deeper (Tunnels 2)
14-year-old Will Burrows has little in common with his strange, dysfunctional family. In fact, the only bond he shares with his eccentric father is a passion for archaeological excavation. So when his dad mysteriously vanishes, Will is compelled to dig up the truth behind his disappearance. He unearths the unbelievable: a subterranean society that time forgot. "The Colony" has existed unchanged for a century, but it's no benign time capsule of a bygone era. Because the Colony is ruled by a merciless overclass, the Styx. Will must free his father--is he also about to ignite a revolution? Deeper will be published in the United States in 2009, at present available by order from the U.K.