Claiming that they needed help to replenish their fuel supply, the Axons landed near a power station on Earth in their organic ship, known as Axos. To the natives of Earth, the Axons looked like beautiful golden-skinned humanoids.
On Axos' approach to Earth, justifiably paranoid government officials fired missiles at it - and, somehow, Axos managed to evade them, possibly by relocating itself in space and/or time. Its approach to Earth caused freak weather conditions including snow and fog. Once it landed, it buried itself deep in the ground, leaving only the opening aperture protruding above. The Axons' first action was to snare passersby with a tentacle that pulled them into the ship. These specimens were examined, and held for further study if they warranted it. Useless specimens, on the other hand, were absorbed, leaving behind only a husk that would disintegrate if touched. The Axons keep their specimens pinned down with large claws to prevent escape, although the ship can be disoriented by a strike to the ganglions that dangle from the walls. The ship itself, Axos, is completely organic, grown from a single cell for the Axons' journey, and seems to breathe through gills on the side.
When they were contacted by UNIT members, the Axons claimed that their worlds, on the far side of the galaxy, had been crippled by solar flares. They needed to replenish their nutrient and energy cycles, and in return for this, they would give the people of Earth a gift - axonite, the source of all their growth technology.
Axonite can absorb, convert, transmit and program all forms of energy - this revelation naturally caused the Doctor to wonder why, then, their ship had been damaged by the solar flares. It is the "chameleon of the elements", a thinking molecule. It uses the energy it absorbs not only to copy, but to recreate and restructure any given substance - yet, as the Doctor speculated, they still ran out of fuel. Axonite also appears to have the ability to grow or shrink objects, even living ones - thus it could end the world's hunger problem.
Naturally, this prospect was hugely appealing to certain people in power. What they did not know was that the Axons had been brought to Earth by the Master. Using axonite, they were able to duplicate human beings, and they also possessed the power to mentally probe and control the people in their ship. Their aim was to spread axonite all over the planet, and thus destroy all life on Earth. Axonite was exploited as bait for human greed - once it had been dispersed around the Earth, the Axons would begin their nutrition cycle and absorb all of the planet's energy.
The Axons' true form is that of a tentacled, reddish-orange creature. In this form, they can launch tentacles at people and stun them, kill them or cause an explosion. They can also melt solid metal.
The Doctor discovered the Axons' true nature and learned that the Axons, their ship and axonite were all one living creature - Axos. The axonite was simply its dormant state, but could be awakened, and the energy from axonite could turn human beings into Axons. The Axons decided that they also wanted the Doctor's assistance to give them the secret of space/time travel. With that knowledge, they would be able to vastly increase the range of their feeding sources. But the Doctor managed to trap Axos in a time loop, and only barely escaped himself.
