The Daleks come to the same conclusion and create two timed explosives to destroy the beacon. One Dalek supervises two humans placing the explosives, but one of the humans, Galloway, secretly keeps one bomb. Two other Daleks enter the city to investigate the superstructure, but the Doctor and Bellal enter the city just before them. The two parties then proceed through the city, passing a series of progressive intelligence tests. The Doctor reasons that the city has arranged the tests so that only lifeforms with knowledge comparable to that of the city's creators would reach the brain, allowing the city to add the knowledge of the survivors to its databanks. On reaching the central chamber, the Doctor begins to sabotage the city's computer brain; the machine responds by creating two Exxilon-like "antibodies" to "neutralise" the Doctor and Bellal. The pair are saved when the Daleks enter and fight the antibodies, and the Doctor and Bellal escape as the city's sabotaged controls begin to malfunction. The two Daleks inside are destroyed.