For Sam, knowing a little about her mother's disappearance through the portal is almost worse than knowing nothing at all. Determined to distract herself, she tries to learn everything possible about caring for the herd on Unicorn Island. But when she and her friend Tuck stumble on a coded verse in The Unicorn Protector Creed, they are faced with an even greater task.

With no way of knowing what's beyond it, Sam, Tuck, and Barloc the unicorn step through the portal and find that not only is Sam's mother no longer a unicorn protector, she also lives in a world plagued by its own problems--and convinced that the only solution to them rests in the horn on Barloc's head.

With the portal closing at sundown on the third day, Sam and Tuck are in a race to rescue their friend, reunite their families, and save another world from a terrible fate of its own making!