"The Doctor's Daughter" is the sixth episode of the fourth series of British science fiction television series Doctor Who. It was broadcast on BBC One on 10 May 2008.

Continuing where "The Poison Sky" left off, the TARDIS takes the Doctor, Martha, and Donna to the planet Messaline. As they emerge from the TARDIS, they are met by soldiers working for General Cobb. The soldiers force the Doctor to stick his hand into a progenation machine, which uses his DNA to generate a female soldier. They are soon confronted by the other occupants of the planet, the Hath. The Hath attack, taking Martha hostage. The female soldier causes an explosion that seals off the corridor they are in, trapping Martha on the other side. The Doctor and Donna are taken to see General Cobb in the command center, and along the way Donna names the woman "Jenny" because the Doctor calls her a generated anomaly.

On the other side of the corridor, Martha tends to an injured Hath and earns their trust. The Hath take her back to their command center. Meanwhile, the Doctor and Donna meet with General Cobb. The General explains that, initially, they were meant to live with the Hath, but a dispute arose over something called "the Source". Both sides believe that this Source is the breath of their Creator, and the Doctor inadvertently reveals its location to Cobb. On the Hath side, Martha also unknowingly interprets the location of the Source and the two sides prepare for battle. Cobb tries to convince them to join the fighting, but imprisons them when they refuse. Jenny uses her feminine charms to incapacitate the guard and they escape their cell.

The Doctor initially dismisses Jenny as an echo of what it means to be a Time Lord, but as they spend more time together he begins to accept her. The Doctor confides privately to Donna that he is resistant to Jenny coming with them in the TARDIS because she reminds him too much of Gallifrey and everything he lost in the Time War. Donna also becomes intrigued by a series of numbered plaques that she notices in each room. When they reach the location of the Source, it turns out to be a terraforming device within a colonising spaceship. Donna realises that the plaques represent the dates each part of the building was completed, which was a mere seven days previous. The humans and Hath have bred so many generations through the progenation machines that their own history has degraded into myth. The original cause of the conflict is determined by the Doctor to have been the death of the mission commander.

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