The Wizard's Scepter (The Keepers, Book 3)

FACING THE GREATEST DANGER OF ALL!
Princess Arenelle, just turned eleven, the age of Magic, has overcome so much in her quest to be the next Imperial Wizard. Now, as the current Wizard grows weaker and the evil Lord Graieconn grows stronger, she must summon all her reserves of intelligence and courage to outwit the vile creatures and twisted Folk who do the bidding of the Dark Lord. They rise up now, legions of them, from the caverns of Darkearth. Driving the forces of Eldearth before them, they seek to capture and extinguish the Scepter of Light, which protects Eldearth from the supreme evil -- Graieconn himself. Nell cannot stop them alone.
Only by teaming with her twin brother, Owen, can Nell hope to defend the Scepter. But Owen is her archcompetitor for the title of Imperial Wizard! Can Nell and Owen put aside their differences and find a way to work together as the ultimate battle looms? Even then, can Eldearth be saved?