Global warming has led to the melting of the polar ice caps. Sea levels have risen dramatically, with devastating effects. Survivors Richard and Amy Webber of environmental pressure group Greenwatch are teaching children the skills they will need to help restore the damaged planet.

Richard and Amy are arrested in a Commission raid on the school, leaving their own children, Greg and Karen, to fend for themselves. They join Ash and Mai-Li to find Goodman, an old associate of the Webbers, at his laboratory within a derelict mill. Goodman recounts the history of Greenwatch, explaining how its outlawed scientists have been blamed for causing the disaster they had tried to prevent, and the children return to the school for medicine to treat his illness.

Goodman is requested to treat an aggressive Japanese leaf worm disease that has apparently broken out on a farm, affecting its crops. After the group arrive, it transpires that the unscrupulous owner of the farm, Harry Fellside, is using illegal, highly toxic nerve agent chemicals to promote the growth of his plants, and ruthlessly forcing his captured 'climeys' (climate refugees) that have migrated from a similarly-flooded France into brutal lives of slave labour exploitation.

The children respond to a distress call from Loppergarth Island. When they arrive, they find Loppergarth Island deserted, save for Gemma, a sleep-deprived young girl in shock after a week of compulsively trying to stay awake. They eventually ascertain that her parents and the rest of the populace have been consuming contaminated gull eggs, causing them to fall under a shared hallucination and gather to become comatose in the village church for an otherworldly crystal entity.

Greg takes a bored Mai-Li and Ash on a boat tour around the nearby islands to avoid staying cooped up indoors. They subsequently receive a morse code message from Paradise Island. Heading there, they discover and attempt to help old island resident Hepzibah McKinley, a scientist who claims to have discovered the secret of cold fusion, and is continuing her father's incomplete research into the subject to try and create greater sources of energy for the remnants of the world.

Amy appears to escape from The Commission's headquarters, and makes her way back to the base in an attempt to be reunited with her colleagues and family. However, she starts to show more unusual concern for the current whereabouts of the two 'senders', instead of her own children.