The Children's Film Unit gives children the chance to learn filmmaking skills. Doombeach began with an improvisation based from some recent news items.

While his mother is having a baby, a social worker suggests a seaside holiday for 12 year old Gavin. It is term time, so he has to attend school but he is sent to a junior school by mistake. His only friend is 8 year old Terri, the tomboy leader of the local 'mafia'.

After swimming at a local beach. Mark, a member of the gang, develops paralysis and the adults diagnose natural causes, but Gavin, who has 'done conservation' at school, suspects pollution.

With the help of their teacher (Glenda Jackson) the children realize that a leak at a local nuclear power station is to blame. Gavin becomes a 'green' campaigner, inciting the kids to strike about their threatened environment. This results in an invitation to put their case on a T.V. talk show.

When Mark dies, the kids know they must prove that the power station is hiding something. Aided by their teacher they visit the power station with a geiger counter...