There is a land beneath our feet, a land of giant caves, simmering lakes, strange creatures and people. For centuries our two worlds - Goneunderland and Upoverland - have co-existed, together but apart. But the discovery of a legendary blue crystal of immense power threatens to put the two worlds on a collision course. Goneunderland’s king, his rebellious nobles, the Luxian priests, and the scheming Lady Euphansia Fish all covet the stone, and a powerful Upoverland energy magnate will stop at nothing to get his hands on this unrivalled source of power. The Knappler, the miner who found the crystal, flees with his treasure to Upoverland hoping for sanctuary. The chase is on.