An introspective young boy, Joseph Coppock squints at the world with his lazy eye. Living alone in an old house, he reads comics, collects birds' eggs and plays with marbles. When, one day, a rag-and-bone man called Treacle Walker appears, exchanging an empty jar of a cure-all medicine and a donkey stone for a pair of Joseph's pyjamas and a lamb's shoulder blade, a mysterious friendship develops between them.