What is the main conflict in Deep Wizardry by Diane Duane?

Deep Wizardry by Diane Duane is the second of a series of stories that follows two young wizards as they discover their abilities and work toward the betterment of all mankind. The Earth and the preservation of all the species on it is the primary goal of wizards worldwide, and as young wizards are at their most powerful in their youth, Nita and Kit are called upon to take on assignments that are perilous and have consequences that ripple throughout space and time.