When 14 year old Amy Parkson (Ellie Hersey) moves to England after a complicated divorce between her mum and dad, she doesn't know if she will fit in. Bullied by her little sister and not having much luck making friends at school, she meets Max (Liam Morgan Souter) - the boy next door - whom she dislikes immediately.
To bribe her into befriending him, Max shows her his family's darkest secret - a magical - yet deadly - yellow creature that they keep in the cellar. Though this strange creature seems incapable of doing anything good, it brings Amy and Max closer together as friends..