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.

At the Commission Headquarters, telepath agent Kurt Glemser interrogates the imprisoned Amy Webber in a malevolent attempt to locate and arrest the missing telepathic children, who he refers to as 'senders'. Amy tries to send a warning message to Mai-Li through her own telekinesis abilities, but she is too late; eventually realising that herself and Ash are in imminent danger, Mai-Li is then faced with altering Goodman's memories before Glemser forces him to betray her.

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.

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.