The three heroes journey into an earthquake-prone area where the apes will be reluctant to follow them. A small number of humans live in the ruins of an old city built some time after the time of Virdon and Burke. Their leader, Green, tells them of the mysterious building which Virdon realises must be a computer centre. He is correct and they find that the equipment still works but before they can make use of it a further earthquake destroys the building and, having enraged Green by entering the forbidden building, they have to leave the city.