Spectrum was founded in 2067 by the World Government to tackle the problem of terrorism still faced by an almost-unified Earth. Headed by Colonel White, a former admiral of the World Navy, it comprises of an elite group of officers known only by their colour codes, and lower ranking agents who retain their own names.

There are Spectrum bases all over the world, but their headquarters is not on land at all: it is 40,000 feet in the air. This floating aircraft carrier is known as Cloudbase, and is home to the highest ranking officers, including Captains Scarlet, Blue, Ochre, Magenta and Grey, and Colonel White's able assistant, Lieutenant Green. The base also houses Spectrum's team of elite fighter pilots. Known as the Angels, they are a ruthless and deadly fighting force to be reckoned with - and are all female.

Although Spectrum's primary objective is to deal with terrorism, they are drawn into the war with the Mysterons by the actions of one of their own agents, Captain Black, and continue with the fight, shielding the world from the terrible truth about these powerful aliens.