Knights from a parallel universe arrive on Earth to find the legendary sword Excalibur. Only the Doctor and Ace with the assistance of Brigadier Lethbridge Stewart can save the Earth from total catastrophe.
Morgaine forces Ace and Shou Yuing to hand over Excalibur by threatening to release the Destroyer, so the Doctor and the Brigadier enter a dimensional portal to stop her.
The Doctor takes Ace to an old 'haunted' house called Gabriel Chase in the year 1883, 100 years before events that took place within that very house in her personal past.
The Doctor and Ace travel to a naval base off the coast of Northumberland towards the end of World War II, where the Time Lord and his companion become entangled in an old Viking curse.
Fenric is loose and planning to use the Ancient Haemovore to poison the Earth with chemicals, unless the Doctor can defeat him in their centuries old game.
A spate of mysterious disappearances in Perivale have been recently taking place, meaning that The Doctor's decision to take Ace to her home village couldn't come at a better time.
The Doctor and Paterson manage to escape from the Master and join up with Ace and her friends, where the Doctor tries to find a way to get them all off the planet before it explodes.
