When Isa Fly appears in the doorway of Captin Len's Fried Fish Shop, thirteen-year-old Ruby is entranced. Isa comes from the coast where the air is fresh; unlike Ruby's home in Cradle Cross, its factory furnaces pumping and filthy slits of canal water sending up a stink. Isa is on the hunt for a missing person, and Ruby is eager to help, convinced she will be repaid with an adventure at sea. But some of the townsfolk are instantly suspicious of the outsider with her shock of white hair and glinting mirrored skirts. They have their own lost relatives to mourn, and don't take kindly to Isa's ability to leave their Ruby spellbound.