What is the main conflict in Song of the Wanderer by Bruce Coville?

Song of the Wanderer: The Unicorn Chronicles, Book Two by Bruce Coville is a book about Cara Hunter and her journey back to Earth from Luster to fetch her grandmother, Ivy Morris. Along the way, Cara learns about her family's mysterious history and their involvement with unicorns. Upon returning to Earth, Cara is confronted by her ancestor, Beloved, who seeks to destroy the unicorns and any world they inhabit. In the end Cara learns about herself, her family, and both the unicorns and the world they now inhabit: Luster.