The TARDIS lands in 22nd century Africa in the shadow of a dormant volcano. Agri-teams are growing new foodstuffs in the baking soil to help feed the world's starving millions – but the Doctor and Rose have detected an alien signal somewhere close by. When a nightmare force starts surging along the dark volcanic tunnels, the Doctor realises an ancient trap has been sprung. But who was it meant for? And what is the secret of the eerie statues that stand at the heart of the volcano?