In the 9th Century, warring factions banded together in Britain to fight a common enemy. After barely defeating it, they chopped its body into three pieces and planned to bury them under perpetual guard at distant and isolated spots on the planet. Two guardians are able to secure their pieces but one is killed en route and his piece is found in an archeological dig on Sheffield Town Hall by Mitch and Lin. The UV light revives the piece and it draws its other pieces to it, causing disruptions at the other two sites. Reunified, it escapes but its absence is noticed and Lin goes looking for it. The T.A.R.D.I.S. arrives to investigate the non-terrestrial signal and the team meets Mitch. When Lin joins them, she tells them about a squid-like creature she found on the wall but it's gone when she leads them back to it. The Doctor takes some goo to test and the archeologists go home to rest. It turns out that the squid creature is attached to Lin and has taken control of her.
The Doctor's tests reveal that the creature is a Dalek and they manage to track its movements. Meanwhile, Ryan's father, Aaron, has returned and is trying to make amends as well as sell a new sort of microwave oven. In their pursuit of the Dalek-Lin, Graham gets left behind with Aaron. Dalek-Lin acquires weaponry and builds itself a new casing. Lin gets rescued.
The final confrontation ends with the Dalek being tricked into getting sucked into a supernova but it tries to take Aaron with it. Ryan saves his father and the team sets off for more adventures.