Cold Blood was the ninth episode of the fifth series of BBC Wales Doctor Who. It was the second part of a two-part story that featured the return of the Silurians and the death of recurring companion Rory Williams, which soon escalated further to total erasure from existence after a crack in time consumed his body. Once more, the Doctor is seen trying to bring about a peaceful solution to a conflict between Silurians and humans. In this case, a rogue Silurian is responsible for the breakdown of trust, as is just one human.
The Eleventh Doctor and Nasreen enter the Silurian city. A curious Nasreen wonders how any of the vegetation and the city itself could be there, being so far beneath the Earth. The Doctor explains that the city and the vegetation are fueled by thermal energy and most of the Silurians are hibernating in suspended animation. Nasreen wonders if waltzing straight into the city is a good idea as the Doctor assures her that the “front door approach” is always the best idea. An alarm goes off, announcing hostile life forms entering the city. Shocked at being called hostile, the Doctor admits that the “front door approach” may not have been the best idea. They turn to leave, but Silurian soldiers arrive and hold them at gunpoint. The Doctor tells them they are not hostile, but the Silurians knock them out with gas.
Amy and Mo are strapped to surgical operating tables in a Silurian surgery. The Silurian surgeon, Malohkeh, is getting ready to dissect Amy. He removes his mask and tightens Amy’s straps. He then takes the scalpel and begins to put it in Amy’s chest, but is called away to examine the Doctor and Nasreen. Amy, who has sneaked the remote controlling the surgical tables from the surgeon, releases Mo and herself and they escape into the city. While searching for a means of returning to the surface, they find Elliot, trapped in suspended animation, but alive.
The Doctor and Nasreen are strapped to tables in a separate laboratory and forcibly scanned; while Nasreen is complacent, the Doctor cries out in pain. Malohkeh converses with Commander Restac, wondering if there has been any word from Alaya. When Restac briskly responds in the negative, Malohkeh assures her that it is all right to show some emotion as they are from the same genetic line. Malohkeh begins to decontaminate the Doctor and Nasreen; again, the Doctor cries out, begging Malohkeh to stop. Because the Doctor is not human, the decontamination process affects him differently — not only does it cause him severe pain, but it removes all of the bacteria keeping him alive. Against Restac’s wishes, Malohkeh agrees to halt the process after seeing an internal scan shows he is not human. He informs a curious Doctor that the drill was threatening the city’s oxygen pockets. The Doctor reveals they have Alaya — also determining from Restac’s reaction that Restac and Alaya are related — and assures the Silurians she is safe. Restac, however, is less inclined to negotiate, and orders the execution of Nasreen and the Doctor out of spite.
On the surface, Tony approaches Alaya for help in curing the venomous sting on his shoulder, promising to release her if she can do something for him. Alaya refuses and amuses herself by having Tony describe what the venom’s effect feels like. Ambrose eventually learns of Tony’s injury and Alaya’s refusal to help. She angrily confronts the Silurian, threatening her with a taser. Alaya encourages her to use it, which she does; on the second shot, Alaya collapses as Tony and Rory arrive, and she dies in Rory’s arms. They both become angry with Ambrose because she killed their only bargaining chip to get their loved ones back. Ambrose expresses remorse for what she’s done.
Restac and Malohkeh lead the two prisoners to the city’s execution chamber, flanked by Silurian warriors. The Doctor explains the nature of the Silurians’ hibernation to Nasreen: centuries before, their astronomers predicted a planet was on a crash course for Earth, so they hibernated below the surface to avoid the catastrophe. The planet was, in fact, the moon coming into alignment. Malohkeh is impressed with the Doctor’s knowledge of their race, prompting the Doctor to reveal that he’d previously met another branch of them. He is less excited to inform Malohkeh and Restac that branch was killed by the humans (specifically UNIT by order of his old friend, the Brigadier), reigniting Restac’s rage. Once inside the execution chamber, Mo and Amy appear, brandishing guns they have taken from sleeping Silurian warriors, with the intention of rescuing the Doctor. Restac swiftly disarms Amy, forcing their surrender. The two are added to the procession. When Malohkeh protests, Restac dismisses him.
On the surface, Rory and Tony berate Ambrose for what she has done to Alaya. Suddenly, Restac’s face appears on the screen of a deactivated computer monitor in the church cellar. She has somehow manipulated the monitor to address the humans and negotiate Alaya’s return. Though the Doctor orders Ambrose to let Rory handle the situation, she steps in and declares she has had enough of the Silurians’ orders. She refuses to return Alaya unless Restac releases her family. Angered, Restac orders the first execution: Amy. The computer monitor goes dark, but before the Silurian warriors can fire, their leader, Eldane, arrives with Malohkeh and countermands the order. He dismisses Restac and her warriors. The Doctor, realizing his chances of negotiating have been reignited, resumes communications with his companions on the surface, ordering them to bring Alaya down via the Silurian transport pods in the mine store room. Reaching the mine, Ambrose encourages Tony to reactivate the drill on a timer in case things go wrong.
The Doctor appoints Nasreen and Amy as the ambassadors for humanity and allows them to talk to Eldane. Meanwhile, he and Mo are led by Malohkeh to the stasis chamber where Elliot is being kept. Malohkeh explains that he doesn’t dissect children, but slows their growth so that he can study how they develop and grow. The boy is released and the Doctor apologises for putting him in harm’s way. Elliot happily forgives him. The Doctor, Mo and Elliot return to the negotiations, but Malohkeh opts to stay behind to check something. He discovers Restac has awoken more of her warriors to stage a coup, but is killed by her before he can warn the others.
Amy, Nasreen and Eldane talk about how the Silurians might be able to live alongside humans. Amy proposes using areas of the Earth uninhabitable to humans as new habitats for the Silurians. With the promise of a place to live, Eldane insists his race can bring new technology and resources. As the meeting concludes, the Doctor comments on how well things have gone.
However, Rory, Tony and Ambrose enter, placing Alaya’s body on the floor. The Doctor is furious with Ambrose, promising Eldane he had no idea of what had happened. Ambrose pleads that she was only trying to protect her family, but it becomes clear that even Elliot and Mo are disgusted with her. Restac returns and cries at the sight of her sister. When she learns Ambrose is responsibile, she orders the woman’s immediate execution. The warriors fire at her, but the Doctor steps in to protect her. The group is forced to flee the room.
Eldane leads the Doctor and his friends to the laboratory. They barricade themselves inside and try to think of a way to proceed. Time is running out before the drill reactivates and destroys the Silurian city, but with Restac’s warriors surrounding them, they cannot return to the surface and turn it off. Restac’s too blinded by rage to realize she’ll die. Eldane decides to use an emergency failsafe. He will use the controls to release a cloud of toxic gas across the city. The Silurians in suspended animation in their cryo-chambers will be safe, but those under Restac’s orders will be killed. The Doctor, with Nasreen’s reluctant permission, agrees to program an energy surge to destroy the drill and prevent any further threat to the city.
Though the Doctor regrets the failure of compromise, Eldane insists the Earth is not ready for the return of the Silurians yet. With this, the Doctor informs his companions that in a thousand years, the Silurians will return to the surface no matter what and they must spread the word. Tony decides to stay behind when he learns that the Silurians can cure his wound, which is causing mutation. Nasreen also opts to remain, thanking the Doctor for helping her fulfil her dream of seeing the Earth. The Doctor ushers his companions to the TARDIS, ordering the Northovers inside and telling them where the medical bay is.
However, he is distracted by the sight of a crack opposite the TARDIS; Amy recognises it instantly. The Doctor is distressed that he doesn’t understand it, especially when he remembers that Prisoner Zero and the Weeping Angels seemed to know what it was. Knowing that the cracks were caused by a temporal explosion, he muses that with an explosion, there is shrapnel, and reaches into the crack; wincing in pain, producing a shard of smoking debris. Before he can take a good look at it, Restac crawls into the room, having let herself be poisoned so she can get her revenge. She aims her weapon at the Doctor, but Rory jumps in the line of fire, taking the hit. Before Restac can fire again, she dies. After a brief conversation with Amy, Rory dies in her arms. The Doctor, seeing Rory has already been surrounded by the time field, forces Amy into the TARDIS, where they watch as Rory is slowly swallowed by the crack.
A devastated Amy reminds the Doctor what he told her after the Byzantium: she remembered the Clerics because she is a time traveler. This, however, is her own history changing, so it’s different. He tries to help Amy remember Rory, which he admits is possible if there is no distraction. As Amy remembers Rory, her memories of him begin to fade. Amy tries her best, but the TARDIS has a bumpy landing that breaks her concentration. She forgets all about him. All that remains of Rory is the engagement ring he gave Amy lying on the floor of the TARDIS console room, and the Doctor’s memories of him.
The Doctor, Amy, Elliot, Mo and Ambrose rush out of the TARDIS to see the drill explode. Some time later, the Doctor encourages Ambrose to bring Elliot up with the best values, so he may represent the best of humanity in the ways that she couldn’t.
The Doctor and Amy return to the TARDIS. Amy stops to wave at her future self on the opposite hill; for a moment, she believes she saw someone else next to her as well, but quickly forgets about it, reminding the Doctor of Rio. Once she is inside the TARDIS, he remembers the debris he pulled from the crack. It is a scorched blue and white fragment of wood with black lettering. The Doctor holds it against the sign on the TARDIS door, confirming it is a broken piece of the TARDIS exterior. The Doctor worriedly enters the TARDIS.