Twelve-year-old Henna is content to live on the island of Earth's End with her fathers, tending her garden and learning about the island's history. However, when one of her fathers falls ill, she leaves her home for the first time to attend St. Basil's Conservatory, a horticulture boarding school in the Gardenia Isles where she hopes to find the seed for a plant that could cure her father. Having grown up an only child, Henna learns about friendship, injustice, and changing things for the better.