1872. After finding a strange signalling device on the moon, the Doctor and Peri travel to the depths of the English countryside to track down the source of its transmissions. But they're not the first aliens to arrive on the scene.
Old enemies of the Doctor are drawing their battle lines in the forest and the local humans will be lucky to escape the conflagration unscathed.
For hidden within this village is a deadly secret - a secret that could destroy the entire Sontaran race... and reveal the terrible mystery of their creation.