Just as people are destined to die once, and and after that to face judgment, so Christ was sacrificed once to take away the sins of many; and he will appear a second time, not to bear sin, but to bring salvation to those who are waiting for him. (Hebrews 9:27-28)
The plot of the Doctor Who episode “The Stolen Earth” is basically what is says on the tin: the Earth has been stolen, right out from under the TARDIS, by the Daleks. While the Doctor and Donna try to figure out where it has gone, the humans stolen along with their planet must deal with their new pepper-pot overlords and figure out how to get back to their rightful location in space and time.
Former Prime Minister Harriet Jones becomes the one who marshals the Doctor’s forces in his absence. She uses a piece of alien technology called the sub-wave network, which allows her to contact everyone who might be able to get in touch with his tenth incarnation: Captain Jack Harkness in the Torchwood hub, Sarah Jane Smith, Martha Jones, and Donna’s grandfather, Wilf, who just happens to have Rose Tyler with him. All efforts to reach the Doctor have thus far been unsuccessful, but together they concoct a plan to boost the signal and get all the phones in the world to call the Doctor’s number at the same time.
There’s a problem, however. All that signal-boosting and transmitting will make the sub-wave network visible to the Daleks, who will promptly find and exterminate them. Yes, Harriet acknowledges, they would see it, but they would trace the signal back to her, thus protecting the others. “But my life doesn’t matter,” she tells them, “not if it saves the earth.”
In the end, the Daleks do find and kill her, but the heroes’ plan is successful. The Doctor finds them, the Daleks are defeated, all of the stolen planets are returned to their rightful places, yada, yada, yada. Harriet Jones’s death helps to save the earth and the day.
At least Harriet Jones was killed by an actual, fearsome enemy, and not by the very humans her sacrifice was meant to save.