Thirteen-year-old Nat is bitter about moving to Mosspond, and the future looks dim until he stumbles across the trail of a strange, ghostly boy--Jude--who is frightening yet intriguing in his cold silence. One afternoon, Nat discovers Jude playing the piano. While listening, Nat is near crippled by the music's profound sadness. When he realizes that the performer of the piece is as tortured as the music he plays, Nat comes to the conclusion that Jude is ill in a sense that cannot be physically explained and undertakes a quest to find the cure for his tormented friend.