The TARDIS arrives in the small Welsh village of Cwmtaff in 2020 instead of Rio de Janeiro which The Doctor had promised Amy Pond and Rory Williams. They discover a mining operation and go off to investigate. Rory notices that Amy is wearing her ring and he doesn't want to loose it so he takes it back to the TARDIS but the other two don't wait for him. When Rory leaves the TARDIS , he is mistaken for being a policeman and taken to a empty grave by Ambrose, a woman and her son.
The Doctor and Amy visit the mining operation which is trying to dig the deepest ever hole, so far 13 miles down. At the site, The Doctor meeting Nasreen who is the leader of the operation. The ground keeps opening up holes in the ground and eventually Amy is caught in a hole and falls through despite the Doctors attempts at rescuing her.
When the Doctor discovers that life forms are coming up from the ground below, he orders everyone into the church for protection. Rory joins them in the church but is shocked not to see Amy. Ambrose's son goes off to get his headphones after the Doctor tells the boy that its ok. The boy doesn't return, he is captured by a figure lurking outside the church.
The Doctor and Rory using a fire extinguisher capture an alien to discover it is a Silurian, a reptilian human from Earths distant past who seems to have woken up. The Doctor smuggles the Silurian into a cellar in the church where he questions the female called Alaya but she's not interested in answering the questions.
Amy awakes to find that the Silurians want to cut her open for dissection like what they had done for the man in the next bay who is Ambrose's husband. Amy is able to see the dissection put off and during the close up, she manages to steal the device that controls the grips that holds her in place.
The Doctor wants to go underground to find the Silurians but Nasreen insists on going. Above ground, Rory is tasked with looking after the Silurian and making sure nothing hurts her and as she could be the person who could the operation become a success or a failure.
The Doctor finds a large Silurian colony, mostly at sleep deep in the underground caves. Continued in Cold Blood