Sara Kingdom

Sara was a dedicated space agent for Mavic Chen, was the sister of Bret Vyon, who she killed in the Daleks Master Plan. Once alerted to Chen's treachery she became a companion, helping the Doctor against the Daleks and she was killed. She was aged to death in seconds by the Time Destructor.

Mavic Chen was a traitorous guardian of the solar system who joined the Daleks, by helping them get the taranium core. The taranium core was the vital element of the Daleks' Time Destructor. The Doctor stole it and the Daleks followed the Doctor through time and space. The Doctor had no choice but to give the Daleks the taranium core. The Daleks eventually exterminated Mavic Chen.

Bret Vyon was also a dedicated space security agent and he joint with the Doctor on Kembel to defeat the Daleks. Having escaped in a stolen spaceship, Bret was shot by his sister Sara Kingdom.

Sara Kingdom was only in The Daleks' Master Plan: The Traitors to The Daleks' Master Plan: Destruction of Time.