A year has passed since Matthew said goodbye to his alien friend, and in the summer holidays he meets Albertine, a mathematical prodigy, with whom he discovers he can communicate telepathically. One day Chocky returns to warn Matthew that they are both in danger. When he returns to tell Albertine, he finds she has disappeared.

A year has passed since Matthew said goodbye to his alien friend, and in the summer holidays he meets Albertine, a mathematical prodigy, with whom he discovers he can communicate telepathically. One day Chocky returns to warn Matthew that they are both in danger. When he returns to tell Albertine, he finds she has disappeared.