In 12th century England, infamous thief baron Irongron attracts the interest of Sontaran warrior Linx, who has unwillingly landed on Earth. To repair his ship Linx must travel through time, entering the realm of UNIT and Doctor Who.

Doctor Who gets a glimpse of a Sontaran warrior and quickly travels back in time to Medieval England. While making the trip the Doctor realizes noise in the compartment is reporter Sarah Jane Smith who due to circumstance, becomes his companion.

The captured UNIT scientists remain in captivity when the Doctor and Sarah arrive in Medieval England. To make matters worse, Sontaran Warrior Lynx requires scientific expertise to repair his ship and thus forms an alliance with chief Irongron.

The Doctor hopes to rescue the scientists but must first face off against Sontaran Warrior Lynx and chief Irongron, both of whom are intent on stopping him. A primitive weapon however, may be the Doctor's only effective strike against the sinister allies.

Rebels capture the Doctor and Romana on a medieval planet ruled by vampires Zargo and Camilla; with Tom Baker.

Ice Warriors send lethal pods to Earth.

Ice Warriors manipulate Earth's weather.

The Doctor and Sarah transport to Exxilon outside a city that seems to live like an organism. Soon after, the Doctor realizes he must find an elusive antidote to defeat a galactic plague spread by the Daleks.

Since the planet Exxilon is futile because of an energy drain leaving TARDIS without power, the Doctor is forced to look for the antidote to a galactic plague. To make matters worse, the Daleks--the creators of the plague--have arrived.

On Exxilon, a war rages between two factions caging the Doctor and Sarah in the middle. Aided by rebel leader Bellal, the Doctor and Sarah continue their perilous search for the cure to neutralize an imminent plague.

An unstable alliance between the humans and Daleks results from their common goal of destroying the 'living city.' Despite their intentions the Doctor has a much safer solution, spoiling the Daleks plan to unleash an apocalyptic plague.

As the New Year begins, a terrifying evil is stirring, from across the centuries of Earth's history; as the Doctor, Ryan, Graham and Yaz return home, they must try to overcome the threat to the planet.