Doctor Who: Colony in Space

The Time Lords discover that the Master has stolen secret information about a device called the Doomsday Weapon and realize they need the exiled Doctor's help. They send the TARDIS, along with the Doctor and his assistant Jo Grant, to the bleak planet Uxarieus in the middle of the 25th century where all is not well.
What is attacking the colonists and can the Doctor stop his old enemy from finding the dangerous weapon before it is too late?

The Time Lords discover that the Master has stolen their secret file on the Doomsday Weapon and decide to send the Doctor to retrieve it for them.
The TARDIS takes the Doctor and Jo to the desolate planet Uxarieus in the year 2472. There they become involved in a dispute between some beleaguered colonists and the crew of an Interplanetary Mining Corporation (IMC) spaceship over the ownership rights to the planet. The Doctor learns that the indigenous Primitives and their High Priests worship a large machine tended by a creature called the Guardian.
The Master meanwhile arrives in the guise of an Adjudicator sent from Earth to decide the fate of the planet. He forces the Doctor to take him to the Primitives' underground city, where they learn that the machine is in fact the Doomsday Weapon, capable of destroying entire planets. Its radiation emissions have brought about the decline of the Guardian's race and are also responsible for the crop failures that the colonists have been experiencing.
The Doctor persuades the Guardian to destroy the Weapon rather than let it fall into the Master's hands. The two Time Lords get clear just in time as the machine explodes, and the Master then escapes in his TARDIS. The colonists, meanwhile, attack the IMC men and force them to surrender.

Directed by Michael E Briant
Written by Malcolm Hulke
Produced by Barry Letts
Original Music by Dudley Simpson
Film Editing by William Symon
Costume Design by Michael Burdle

First Transmitted
1 - 10/04/1971 18:10
2 - 17/04/1971 18:10
3 - 24/04/1971 18:10
4 - 01/05/1971 18:10
5 - 08/05/1971 18:10
6 - 15/05/1971 18:10

The TARDIS materialises and dematerialises instantaneously, rather than fading in and out as usual.

Mary Ashe is played by Helen Worth, now best known for her long-standing role in Coronation Street.

The Master's TARDIS is now disguised as the Adjudicator's spaceship and its interior is seen for the first time (barring a tight shot of one wall seen on a screen in Terror of the Autons).