High Wizardry (The Young Wizards Series, Book 3)

Don't take brilliant, shrewd Dairine Callahan for just any bratty younger sibling. Impatient for adventure, knowledge, and recognition, she finds her sister Nita's wizardry manual and reads the Oath aloud. Disappointingly, nothing happens. But when her family's new computer arrives, Dairene discovers more than the standard issue system software on it and launches herself on a reckless, universe-wide, high-voltage magical conflict with the Lone Power. Diane Duane's storytelling is skillfully mythic and wittily referential; Dairine's discovery and shaping of a new form of life is wondrous. For maximum enjoyment, read So You Want To Be A Wizard and Deep Wizardry first.