Orla has been on her own since Ma died, living in a woodshed by the river, with only her beloved garden for company. It provides all she needs. But when sickness comes to the land, Governor Atlas decrees that plants are the cause, and must be destroyed. Armed with her mother's book of remedies, Orla steals away on a river boat, setting off to discover the truth and save her garden. But she's not the only stowaway. Soon she, Idris and Ariana must navigate the rapids of the Inkwater to a poisonous place from which they may never return . . .