It is a history book. The protagonist is Tom, a young chimney sweep, who falls into a river after encountering an upper-class girl named Ellie and being chased out of her house. There he drowns and is transformed into a 'water baby', as he is told by a caddisfly-an insect that sheds its skin—and begins his moral education. The story is thematically concerned with Christian redemption, though Kingsley also uses the book to argue that England treats its poor badly, and to question child labour, among other themes. Tom embarks on a series of adventures and lessons, and enjoys the community of other water babies once he proves himself a moral creature. The major spiritual leaders in his new world are the fairies Mrs. Do as you would be done by (a reference to the Golden Rule), Mrs. Be done by as you did, and Mother Carey. Weekly, Tom is allowed the company of Ellie, who did not drown after he did. Grimes, his old master, drowns as well, and in his final adventure, Tom travels to the end of the world to attempt to help the man where he is being punished for his misdeeds. Tom helps Grimes to find repentance, and Grimes will be given a second chance if he can successfully perform a final penance. By proving his willingness to do things he does not like, if they are the right things to do, Tom earns himself a return to human form, and becomes 'a great man of science' who 'can plan railways, and steam-engines, and electric telegraphs, and rifled guns, and so forth'. He and Ellie are united, although the book states that they never marry.