Railsea is a young adult novel by China Mielville. It details the journeys and exploits of Sham Yes ap Soorap, a boy somewhere in his late teens, as he lives his life on the railsea. When the novel begins, Sham is a doctor’s assistant on board the Medes, a mole-hunting train, captained by Abacat Naphi, who has her eyes set on one goal in life –to hunt down and destroy Mocker-Jack, a massive moldywarpe. Sham is not thrilled with his work, though, and believes he may want to be a salvor, to collect salvage instead. While exploring the wreck of an old train, Sham discovers a camera's memory card which has photographs that depict a boy and a girl and a single rail line that leads across empty ground –a stunning sight.

Sham ultimately tracks the boy and girl down –Dero and Caldera Shroake –whose parents were lost at railsea years before. They decide to set out to see what their parents wanted to see. They ultimately end up on the Medes. After battling pirates, a rogue naval train, and angel trains, the Medes heads out across a bridge which crosses a deep gorge. Continuing on by foot, Sham, the Shroakes, and Naphi discover an old town where the rail lines end. The town is where companies built rail lines all across the world to compete and make money eons ago. It ultimately collapsed, leaving the rails behind. On the other side of the town is an ocean that has been blocked off by a massive dam. Ultimately, Sham, Naphie, and the Shroakes decide to sail across the ocean to see what is on the other side.