Henry van Statten: There has to be something it wants.
The Doctor: What's the nearest town?
Henry van Statten: Salt Lake City.
The Doctor: Population?
Henry van Statten: One million.
The Doctor: All dead. If the Dalek gets out, it will murder every living thing. That's all that it needs.
Henry van Statten: But why would it do that!?
The Doctor: Because it honestly believes they should die. Human beings are different, and anything different is wrong. It's the ultimate in racial cleansing, and you, van Statten, YOU'VE LET IT LOOSE!