Harriet Ambrose, a government technician, is travelling from London to Sheffield, aware of a pending cataclysm. As the train she is on enters a tunnel, a meteorite the size of Birmingham strikes the Earth.

The survivors explore the ruins of Sheffield city centre in a search for friends and family, but find no survivors. The group desperately needs to find a supply of fresh water, and Harriet leads them to the bunker, and possible salvation. They are confronted by evidence of fellow survivors, but it is of an unwelcome nature.

The survivors reach the Ark, where they discover the truth about Hild's people.