Defeated time and again by Earth's heroic X-COM forces, aliens from three different civilisations join forces and seek a new conquest - the World of Two Moons. However, one important fact has escaped their attention...

...they are not the first aliens to set foot on this lush, vital new world. Ten thousand years ago, a vessel carrying otherworldly explorers was forced down in the midst of the planet's ice age. The stranded newcomers, possessing near-magical powers of the mind but finding them crippled by the planet's aura, were forced to take drastic action to survive and, as the centuries passed, they became legends.

Humanity on the World of Two Moons, which they call "Abode", is now on the verge of taking that first step towards industrialisation, and the alien forces feel the time is right to take the first steps towards invasion. Unknown to the alien hordes, the legacy of X-COM has followed them. One man who is not entirely human, separated from his colleagues in the final battle of 2084, has found his way to Abode, and knows the horrors awaiting this unsuspecting planet.

And so, it begins...