One fateful night, the moon shines so big and so bright that it is too heavy to hold itself up in the sky. When it tumbles down and breaks into many glimmering pieces, Luna sees the whole thing. Her grandfather Poppa warns that without the moon in the sky, the oceans will stop moving and the earth will start to wobble. Luna and Poppa must mend it, but they may not be able to do it all on their own. The mountain is alive with creatures big and small whose watchful eyes also saw the moon fall.