Michael Ellis has just moved with his parents and baby sister from London to a rambling Victorian house in Yorkshire. Not being able to sleep on his first night, Michael goes downstairs to get a glass of water from the kitchen, where he makes the most amazing discovery. Standing on the draining board is a small furry elf-like creature which not only has the ability to change its size, but can also talk as well! Michael learns that the creature is called Gwoppy and they soon become firm friends. A series of adventures follow with Gwoppy meeting an escaped lion as well as taking a ride on a whooper swan. But can Gwoppy, with Michael's help, rescue the family of doormice from the black rat who is threatening to evict them from their home?