'Ten years ago Rab learned the secret of the planet he calls home – and lost the young girl he’d vowed to protect; traded for a sweater, a set of gloves and a second-hand pair of boots. Since then, he’s wandered the barren surface alone searching for her, returning to the tunnels only when hunger, exhaustion or the inconstant seasons offer him no choice. When a freak accident occurs during the harvest, the death of an old friend finds Rab agreeing to abandon his search and guide Fin, now a tunnel-dweller, and Cloud, a former captive of the Top-siders, back to his old village to deliver a macabre and precious cargo. Although reconciled to honouring his word, Rab is convinced that their reckless journey south will tell him nothing he doesn’t already know and that the secret he has dutifully guarded all these years is in no danger of being exposed. He is wrong.'
Source: Publisher's blurb.