The events of the novel take place in post-nuclear Rostov — but the setting is not all that important in this novel. The same tragedy could have unfolded in any other city in Russia — in the Metro Universe.
The main character, Ilya, having lost his entire family to a monster invasion due to an act of betrayal, finds himself alone against a terrifying new calamity that could destroy the entire city, wiping from the face of the Earth and tearing from its depths not only people, but all living things.