Chocky is invisible, clever — and from another planet. She is an unseen companion for 14-year-olds Matthew and Albertine. Chocky brings them knowledge of life in a distant world, one with much to give to those on Earth.
Chocky seeks to pass on the secret of unlimited energy. The children are ready to receive it for the benefit of all mankind, but powerful military and business interests want it only for themselves. If they don't get it, they will destroy it — and with it, if need be, Chocky herself.