The sequel to the New York Times Bestseller! Searching the bowels of the earth for his lost dad, Will stumbles across the Styx's diabolical plan to extinguish all Topsoilers. Dig DEEPER!

In TUNNELS, boy archaeologist Will Burrows went in search of his missing father--and discovered a sinister subterranean world. Now, wandering the dark, hot bowels beneath the Colony with his best friend, Chester, and his brother, Cal, Will stumbles across the Styx's dastardly plan to exterminate all Topsoilers by unleashing a lethal plague. Slowly he begins to piece together the plot. But how can Will save the Topsoilers from annihilation when his own life is at risk--and his killer stepsister is still at large?