The 16-year-old Keeper of the Isis Light, Olwen Pendennis, and her companion, Guardian, have lived alone on the remote planet of Isis since the death of Olwen's parents.

Now, colonists from overcrowded and polluted Earth have arrived to settle in Isis' unspoilt valleys.

Conflict arises as the new inhabitants start to repeat the mistakes of past generations and Olwen fears they may ruin Isis forever. This is a classic work of science fiction, full of drama and tension.