The Doctor, Amy and Rory land in the small Welsh village of Cwmtaff in 2020, as opposed to their intended destination of Rio de Janeiro. They encounter a mining operation, led by Doctor Nasreen Chaudry, studying minerals deep in the earth that have not been seen for over 20 million years. Nasreen is accompanied by a local, Tony Mack, whose daughter and grandson, Ambrose and Elliot, are examining the disappearance of bodies from underground at the graveyard of a nearby church. An earth tremor causes the ground to open and send Tony and Amy falling into it; Tony is rescued but Amy is pulled under by unknown forces. The Doctor surmises the minerals form a bio-reactive defense system that was triggered by the drilling operation. The group is soon alerted to the presence of three life forms traveling up the drilling shaft from 21 kilometres below the earth, and they barricade themselves in the church. The Doctor explains Amy's disappearance to Rory and assures him he will get her back.
The three beings turn out to be reptilian humanoids, and in a scuffle, they capture Elliot and strike Tony with a venomous forked tongue; the Doctor and the group are able to subdue one of the beings while the other two retreat with Elliot back into the earth. The Doctor realises the beings are a new form of Silurians, and that they have relented in their attack since both side hold a hostage. The captured Silurian calls herself Alaya, a member of the warrior caste awoken by the intrusion of the drill. Alaya believes, as with all the other Silurians, that the Earth still belongs to them and will defeat humanity eventually. Tony, suffering from the effects of the venom, believes they should dissect Alaya, but the Doctor warns that it will be seen as an act of war. The Doctor decides to travel in the TARDIS down the drilling shaft to talk to the rest of the Silurians and work out a truce, with Narseen desiring to come along.
Amy awakens to find herself strapped to an examining table, near to where Ambrose's husband Mo is similar ensnared. Mo apologizes to Amy that the Silurians intended to vivisect them. The Doctor and Nasreen descend in the TARDIS, where the Doctor explains the Silurians and that he only expects to encounter a small number of the aliens. The show ends on a cliffhanger as the Doctor and Nasreen are surprised to find an immense Silurian civilisation stretching out for miles in the caverns below the earth.
* Matt Smith (Eleventh Doctor)
* Karen Gillan (Amy Pond)
* Arthur Darvill (Rory Williams)
* Neve McIntosh – Alaya
* Meera Syal – Nasreen Chaudhry
* Robert Pugh – Tony Mack
* Nia Roberts – Ambrose
* Alun Raglan – Mo
* Samuel Davies – Elliot
Writer Chris Chibnall
Director Ashley Way
Script editor Lindsey Alford
Producer Peter Bennett
Executive producer(s) Steven Moffat
Production code 1.8
Series Series 5
Length 45 minutes
Originally broadcast 22 May 2010