Sara Kingdom, along with her brother, Bret Vyon, are Space Security Agents who join the Doctor in trying to defeat the Daleks in The Daleks' Masterplan. Sara is by turns aggressive, independent and ruthless in her pursuit of what is right. Perhaps a little too ruthless and determined as it turns out.

Sara believes Mavic Chen, the Guardian of the Solar System, when he tells her that her brother Vyon is a traitor. She obeys his order to shoot her brother and then turns her gun on the Doctor and Steven.

Before she can shoot, however, the three of them are transported to another planet, and to her horror, she learns that it is in fact Mavic Chen who is in league with the Daleks, and she has unjustly killed her own brother because of her blind obedience. She then joins the Doctor in his TARDIS to return and defeat Mavic Chen and the Daleks.

When the Doctor activates the Time Destructor,a device that accelerates time, as part of his plan to stop the Daleks, he orders his companions back to the TARDIS for their protection. However, Sara follows him, not knowing the nature of his plan but concerned it might fail. As a result, she is caught in the field of the Time Destructor as it rapidly ages everything around it. While the Doctor, being a Time Lord, can withstand the effects, Sara, being human, cannot. As Steven and the Doctor watch helplessly, Sara ages and dies, her remains aging to dust.