At the heart of the ruined city of Arcopolis is the Fortress. It's a brutalstructure placed here by one of the sides in a devastating intergalactic warthat's long ended. Fifteen years ago, the entire population of the planet waskilled in an instant by the weapon housed deep in the heart of the Fortress. Nowonly the ghosts remain. When The Doctor arrives, determined to fight his waypast the Fortress's automatic defenses and put the weapon beyond use, he soondiscovers he's not the only person in Arcopolis! What is the true nature of theweapon? Is the planet really haunted? Who are the Eyeless? And what will happenif they get to the weapon before the Doctor?