"But for a thousand years the clans have been united under one all-powerful leader—the Keeper of the Crystal. The first Keeper was a man called Orin the Wise. It was he who found the Crystal, a treasure of great power and mystery, in a cave beneath the Maris sea."
The Crystal is a magical stone of great power, wielded by the Keeper of the Crystal, which protects the Maris from invasion by the Zebak. When the current Keeper is dying the light of the Crystal weakens, and a new Keeper must be selected by the Chooser before the light dies away completely. The Crystal also has the power to control the winds and the tides.
Rowan discovers that the Choosers have been members of his mother's family since the tribe who used to choose were decimated by the Zebak prior to the warrior slaves turning against their Zebak masters. This cruel act was the chief factor that prompted the slaves to rebel and join forces with the Travellers and the Maris. Lieth, Rowan's ancestor, took the burden as keeper upon himself and his descendants. Rowan travels to Maris with his mother, Jiller, to take over as Chooser if his mother is killed, as has happened to many Choosers in the past. Rowan recalls what he had been taught about the Crystal, but also learns much more. He learns for instance that each new Keeper has added to the wisdom of the Crystal, yet more recently the candidates have been trained only to gain the Chooser's trust, and have little to add to the power of the Crystal. He also learns that it does not matter from what tribe the Keeper comes, for the Crystal will overcome any loyalty or treachery.