Parts: 1 (45-minute)
Writer: Stephen Greenhorn
Airdate: 10 May 2008
Production Code: n/a

Doctor: tenth
Companion: Donna, Martha

Creature Feature: Hath

Story: The TARDIS hurtles through time and space as if drawn by an external force, finally landing in an underground city on the planet Messaline. The Doctor, Donna and Martha find themselves in the middle of a battle zone; war has been raging on Messaline for generations, between the descendants of the original human and fishlike Hath colonists. Both sides are determined to gain control of the city and the legendary relic that is hidden somewhere deep within it. But the Doctor barely has time to decide how to help out; within moments of their landing, the Hath attack, kidnapping Martha just before the humans seal off the corridor with a massive explosion.

The Doctor and Donna refuse to consider Martha a casualty of war, and insist on tracking her down somehow. But another matter distracts the Doctor's attention, for among the human soldiers is a young blonde woman whom he introduces as his daughter. While Donna tries to help the Doctor come to terms with his newfound kinfolk, the Doctor is more concerned with the fact that despite their blood ties and her sunny disposition, Jenny seems to be a hardened soldier, perfectly willing to murder the Hath in order to help the humans secure the city for themselves. And when the Doctor uncovers a complete map of the city, the race is on: the humans and the Hath are determined to be the first to locate the lost temple, while the Doctor, Donna and Martha try desperately to bring peace to both sides and keep either faction from committing genocide.