In Tunnels, boy archaeologist Will Burrows went in search of his missing father - and discovered a sinister subterranean world. Now wandering the dark, dry bowels beneath the Colony, Will stumbles across the Styx's diabolical plan to exterminate all Topsoilers. Slowly, he begins to piece together the plot. But how can Will save all those above from annihilation when his own life is at risk down below - and when his killer sister is still at large?