The survivors of a devastated future Earth lie in suspended animation on a great satellite. When Earth is safe again, they will awaken. But when the Fourth Doctor, Sarah and Harry arrive on Terra Nova, they find the systems have failed and the humans never awoke.

The Wirrn Queen has infiltrated the satellite, and laid her eggs inside one of the sleepers. As the first of the humans wake, they face an attack by the emerging Wirrn.

But not everyone is what they seem, and the only way the Doctod can discover the truth is by joining with the dead mind of the Wirrn Queen. The price of failure is the Doctor’s death, and the end of humanity.