The Chameleons believe themselves to be the most intelligent race in the universe - even the animals on their home planet are apparently the intellectual equals of Earth people. But their planet suffered a catastrophic gigantic explosion, which caused the Chameleons to lose their identities and their race to begin dying out. Their current appearance is apparently a marked change from their previous form - now they have knobbly skin, and no facial features at all - simply a lumpy head covered in veins. In this form, they have difficulty walking unsupported. The atmosphere of their home planet is different from that of Earth's, and in their featureless form, the Chameleons need to breathe it - the atmosphere of the Earth gradually suffocates them. Their scientists, however, developed a method that enables them to take on the physical characteristics, and memories, of other beings.
In order to carry out this procedure, the Chameleon is first injected with a substance - possibly to revive it from a form of stasis, or to help it survive in the Earth's atmosphere. It is then taken from a cabinet, in which the atmosphere of its home planet has been maintained, to an operating room. Here, the Chameleon lies on one couch while the human whose bodyprint it is about to receive lies on another. A black armband is attached to the Chameleon, and a white armband is attached to its template. Wires connect each of these armbands to a central machine which, when activated, causes the human to spasm as its features are copied to the Chameleon, whose breathing and movements become much more relaxed. At this point, the Chameleon gains the ability to see, speak (using a dial on the armband to adjust its voice and make it more clear) and feel pain. In this form, they possess superhuman strength, and while the process is not always successful at copying accents, otherwise it is near-perfect. The originals, whose identities have been taken over, are kept in a secret location - individual cars in the massive Gatwick Airport car park, or seated in boxes to be transported to the carpark - and only the nurse in charge of the transformations knows where her original is, because she keeps it in the laboratory. While the Chameleons can be processed more than once, to take on different identities, they can only do this with the help of the machine in the medical centre. If the white armband is removed from the template, then the Chameleon possessing that identity turns into nothing more than a blob, and the human recovers.
The Chameleons can be rather sadistic - rather than killing their enemies directly and being done with it, they prefer to give a slow, torturous death, if possible. Their arsenal of weapons seems to favor primarily two forces: electricity and cold. Their most common weapon is a pistol that electrocutes its victim, scorching the clothes. A similar weapon is built into their aircraft, with targetting so precise that it can strike a man between the eyes. They equip their secure areas with nozzles which emit a cold, suffocating vapor. They frequently use a silvery pen-like device, which freezes liquid and temporarily disables and paralyzes people, even after they regain consciousness. They also possess powerful laser cannons, which emit a small but deadly beam, and a button-like device, activated using a small black box, which can be attached to clothing and apparently burns its victim.
Because of the needs of so many people on their home planet, the Chameleons have chosen to abduct 50,000 young people from Earth which they can use as templates. To this end, they started Chameleon Youth Tours, offering budget student trips to destinations like Dubrovnik, Athens and Rome. Travellers are asked to write postcards to their parents before departure (because of course that's the first thing they'll want to do upon arriving, and they may be too busy) which the Chameleon Tours employees collect upon boarding. But the Chameleon Tours planes are, naturally, no ordinary planes: they are equipped with non-terrestrial controls. The passengers are served a meal upon takeoff, which apparently contains some kind of compound to aid in the Chameleons' plans. Once the meal is finished, and the plane has achieved sufficient altitude, the pilot pulls a lever, and all the passengers are miniaturized in their seats. The flight attendants take segmented boxes and collect all of the miniaturized teenagers for storage in suspended animation inside the massive Chameleon space station, hovering 150 miles above Earth. In order to reach it, the Chameleon planes can convert into rockets, which deviate from the scheduled flight path to go straight up through the Earth's atmosphere and into space.
Ultimately, the Doctor is able to find the Chameleons' originals, and threatens them all with destruction unless they return all the miniaturized teenagers back to Earth and restore them to their proper size. With this done, the Chameleons return to their home planet, and the Doctor offers to give their scientists some suggestions on how to solve the Chameleons' problem.
