Kembel

Kembel was a jungle-covered world near the edge of Earth's galaxy. It was considered the most dangerous planet in the universe.

Use as a Dalek base
The Daleks reasoned that the most dangerous planet in the universe, where no one would voluntarily land, would make for the ideal base. (DW: Mission to the Unknown) It was not far from the nearly as hellish Desperus, a penal colony for prisoners. (DW: The Daleks' Master Plan) They transplanted deadly Varga plants from their home planet of Skaro to help guard the place. They also established a Dalek city with its own spaceport. Prior to 4000, a Galactic Council of representatives of the Outer Galaxies, allied with the Daleks, met in order to work out a plan to destroy the Solar System, and in particular, Earth.

Following up a sighting of a Dalek ship near the planet, SSS agent Marc Cory had set up an expedition to Kembel. He learned of the Daleks' plan, but the two crew members of the ship which landed on Kembel were transformed into Varga plants. The Daleks found and killed Cory himself before he could launch an orbital distress beacon so as to warn the galaxy. (DW: Mission to the Unknown).

By a coincidence, before landing there, the TARDIS had earlier materialised near Kembel before landing there later. It appeared on the TARDIS scanner screen and Vicki speculated on what might occur there. (DW: Galaxy 4) Later, not knowing of the planet or its reputation and having landed the ship at random, the Doctor arrived with his companions while looking for help for Steven Taylor, who had recently suffered an infected wound. They learned of the Daleks' plan, and, just as importantly, of the betrayal of the traitorous Human Guardian of the Solar System, Mavic Chen. Chen had given the Daleks the taranium they needed to power their Time Destructor. (DW: The Daleks' Master Plan)

Devastation of Kembel
After being pursued across space and time by the Daleks, the Doctor and his friends returned to Kembel. The Time Destructor was activated, and began to slowly accelerate time around Kembel, turning the jungle into a desert wasteland. The Time Destructor eventually burnt itself out, leaving Kembel a wasteland. (DW: The Daleks' Master Plan)

Behind the Scenes
Kembel first appeared in the last few minutes of Galaxy 4 as a lead-in to Mission to the Unknown, which did not feature the Doctor or any of his companions. Following Vicki's statement, a short "teaser" scene to the action of Mission to the Unknown followed.