Albertine is studying at Cambridge University where she is excelling herself. She wishes to research about cosmic energy, but she meets resistance from Professor Ferris who is fascinated about her theories. Albertine uses an illegal radio telescope to carry out research, but she is discovered by Dr Liddle, who doesn't enjoy her presence. Chocky returns to reveal that her people are prepared to reveal the secret of cosmic energy to the human race.

Matthew receives an art scholarship. Meanwhile, Chocky contacts other children from around the world who she wants to build some equipment that can harness cosmic energy. Albertine is joined by Mike and Su Lin who help her with her research, but she is later joined by the mysterious Paul.

The children start building the equipment based on Chocky's instructions, though Professor Draycott is strongly protesting. He is worried about funding and thinks that it is a waste of money. Draycott is not convinced that they are doing something worthwhile so he sets them a deadline.

It is the demonstration of the new equipment, but some of it has mysteriously disappeared and the research grant has ran out. But Meyer receives a visit from Mrs Gibson who claims to represent the Ministry of Science and she makes an offer to fund further research. Albertine and her father discover a sleepwalking Paul in the middle of the night and he is found to be tampering with the rebuilt equipment. It is revealed that Mrs Gibson's real name is Major Gibson. Major Gibson is working on behalf of an army general who has his own designs for the project.

Major Gibson watches closely as work continues on the next stage of the project. Paul runs away and Albertine tries to pursue him. He leads her to his mother's house where Albertine discovers that his mother is in fact Dr Liddle. Paul has been giving her the details of the project and she believes their proof. Gibson reveals to Meyer and the children that he wants to take over from them and use what they have so far.

Gibson steals a vital part of equipment which he puts into a crate in which Chocky and Paul are also trapped. The crate is moved to a military base. The children discover that Chocky has vanished and so they make contact telepathically with Matthew who returns to help them. Together they project their collective mind to Chocky's home planet across the universe. Another of Chocky's kind helps the children in their search for Paul and he visits Earth. Together they find Chocky and Paul trapped inside the crate at the military base. Gibson is arrested and Chocky returns to her home world. The team are left to continue their work to help the rest of the telepathically sensitive children around the world.