Billy is struggling at school. He's being picked on by the school bully and he's starting to feel very alone. His mum is sick, although nobody seems to know what's wrong with her. She has been sick for a long time meaning that she can't work, so Billy's dad is working extra hours to try to keep the family afloat and Billy is frequently left to fend for himself. His only escape is in watching his favourite, David Attenborough, or in swimming in the sea. One day, however, things take a magical turn as whilst swimming Billy meets a mackerel who speaks to him! This, combined with the entrance of a new boy at school, starts to change Billy's life in some rather unexpected ways.