It was to be a match of human skill and muscle against rocks and cataracts, shut in from the outer world, always face to face with the Shadow of Death.

It was to be a duel to the finish between the mysterious torrent on the one side and a little group of valiant men on the other.

Never had plumed knight of old a more dreadful antagonist.

Like the Sleeping Beauty, this strange Problem lay in the midst of an enchanted land guarded by the wizard Aridity and those wonderful water-gods Erosion and Corrasion, waiting for the knight-errant brave, who should break the spell and vanquish the demon in his lair.

No ordinary man was equal to this difficult task, which demanded not alone courage of the highest order, but combined with this courage a master-mind and the strategic skill of a general.