Deep below the Earth’s surface, Amy (Karen Gillan) and Mo (Alun Raglan) escape from the Silurian doctor Malohkeh (Richard Hope) before they can be dissected, and Mo finds his young son Elliot (Samuel Davies). The leader of the Silurian Warriors, Restac (Neve McIntosh) wants the Doctor (Matt Smith) and geologist Nasreen Chaudhry (Meera Syal) executed. All of the humans are tried and found guilty, but the powerful leader Eldane (Stephen Moore) stops the trial.

The Doctor contacts the surface. Rory (Arthur Darvill), Ambrose (Nia Roberts), and Tony (Robert Pugh) are told to keep the Silurian hostage Alaya (also Neve McIntosh) alive, as she is Restac’s sister, but it seems Alaya is already dead. Desperate, they set the deep-core drill to burrow into the oxygen pockets of the underground city.

Restac is organizing a coup on behalf of the Warrior Cast. The Doctor escapes with the humans and channels an energy pulse to the drill. The Warriors go back into hibernation and the humans escape. Perhaps in a thousand years there might be peace between the humans and the Silurians. The Doctor, Amy, and Rory find a crack in the cavern wall like those we have already seen, left by an explosion in Time. The Doctor pulls something out of the crack. A dying Silurian fires at the Doctor, but Rory takes the shot, dying in Amy’s arms. He is absorbed by the crack and is erased from memory. The object pulled from the crack is a piece of the TARDIS.

The underground Silurian city was beautiful and impressive. Rory’s death scene was difficult for Karen Gillan to do. Neve McIntosh, who played both Alaya and Restac, returns in later episodes as the Silurian Victorian Madame Vastra, a great character who becomes an ally of the Doctor. The Silurians went into hibernation originally because they believed a planet would collide with Earth. Actually, that was the creation of the moon.