Twelve-year-old Henna loves living with her two papas and cultivating her plants on the tiny island of Earth's End - until Papa Niall grows seriously ill. Now Henna is determined to find a legendary, long-extinct plant with miraculous healing powers, even though the search means journeying all the way to St. Basil's Conservatory, a botanical boarding school rumored to house seeds of every plant ever grown. At St. Basil's, Henna is surrounded not only by incredible plants, but also, for the first time, other kids - including her new roommates: wisecracking, genderfluid P and wealthy, distant Lora. But Henna's search for the fabled healing seed means she doesn't have time for friends - or so she thinks.