The Castor, a vast starship, seemingly deserted and spinning slowly in the void of deep space. Martha and the Doctor explore the drifting tomb, and discover that they may not be alone after all... Who survived the disaster that overcame the rest of the crew? What continues to power the vessel? And why has a stretch of wooded countryside suddenly appeared in the middle of the craft? As the Doctor and Martha journey through the forest, they find a mysterious, fogbound village - a village traumatised by missing children and tales of its own destruction...