They appear before Charles Forbin and his friend Edward Blake in the form of two black spheres, and quickly demonstrate vast intellect and powers of transformation and telepathy.

In order to proceed with construction of the "Collector" designed to harvest the oxygen, the Martians reactivate the parts of Colossus necessary to manage human society.

As construction of the Collector proceeds, a humbled Blake proposes to Forbin that the old Colossus — the "parent" of the crippled system, be reactivated.

With his new secretary, a fervently devout woman named Joan, he flies to Portsmouth and takes command of the battleships stationed there for the Sea War Games.

Regaining control of the nuclear arsenal, Colossus contacts the Martians, who inform it of Forbin's attempt to use the battleships to destroy the Collector.