The Doctor and Nasreen are captured by Silurian soldiers when they enter the city. Meanwhile Amy and Mo are able to escape from the lab and discover just how many Silurian soldiers live beneath the earth. They also Mo's son Elliot but they can't wake him up. When they try to free the Doctor and Nasreen, they are captured as well. The military leader threatens to kill them, when Rory and the others don't return Alaya but they can't because Ambrose has killed her. Amy is saved by the leader of the Silurians and she and Nasreen negotiate with him about the future of the humans and Silurians on the surface of the Earth. Everything seems to be lost when Rory and the others bring Alaya's body down into the city of the Silurians but the Doctor and all humans are able to escape into lab. They are searching for a way to get back up onto the surface before the drill explodes but do they have enough time?
This episode is a great second part for this story although it has a quite sad ending. It seems like it wasn't the right time yet for the humans and Silurians to share the surface of the Earth. They are quite similar in many ways but the difference are still to big to live together peacefully. I liked the Silurian doctor a lot and was a bit sad when he was killed while he tried to save the humans. You can see that the Doctor wants to think the best of humanity but sometimes he gets disappointed by what they do. Compared to the Doctor, humans are still children and have to learn so much before they can accept other races. The Silurians looked brilliant again and their city under the earth is an amazing place. A really great episode where the cracks appear again. That's another big mystery for the Doctor to solve.