Shortly after returning from Lurkur Woods where they saved the mysterious sacrosite known as the White Tree, the "impossible" twins, Cynthia Summers (a black girl) and Kaden Krossway (a white boy) must again travel across worlds, this time to save the Lurkur Witch known as the Lil of Lurkur. But their journey takes an unexpected turn when they are sent to retrieve a mysterious and powerful substance known as the Seventh Water. But acquiring it means surviving the Test of Six Waters, which is in fact comprised of six separate missions, each one more daunting than the last, testing them mentally, emotionally and magikally.