As the Time War rages, Cardinal Ollistra of Gallifrey seeks to create ever more dangerous weapons to deploy against the enemy. When the Doctor stumbles across Synthesis Station, he discovers that the Time Lords have sponsored a project to weaponise already-lethal creatures. But in doing so, Eva Morrison and her team have unwittingly used a colony of Vashta Nerada with a very unfortunate history of humanoid contact. The Doctor finds himself leading a desperate race for survival, in which the shadows may be the least of their worries…