By playing UFO 1 and interrogating captured aliens the player was continuously revealing, that the organization Counter alien forces of the Earth failed to stop alien invasion to the Earth and that the Earth was occupied by aliens. He found out, that people of the Earth had been enslaved and had become newly subjugated members of the alien society. Earth became part of the alien empire. After that, aliens attacked Esperanza. However the Counter alien forces of the Esperanza repelled the aliens from seizing their planet. By playing UFO1 the player built on the planet Esperanza spaceship Centaurus and then flew from Esperanza to the Earth to free Earth from alien's grip. The mission was successful and the Earth was freed. Since then, the people of the Earth like a Phoenix rises from the ashes and ahead of the Earth lies promis of the new beginning. That is where the story of the UFO 1 ends.
At this very moment we turn back the wheel of time to the times when the Earth did not even imagine that there were any aliens planing invasion to the Earth although some engineers commonly considered as weirdos sensed, that next challenge for the Earth will come sooner or later from deep space. By playing the UFO2 the player will face to alien's attempt to occupy the Earth and will try somehow to save the Earth and stop aliens from seizing it. His research will tell him what to do. Stories of the UFO1 and UFO 2 are tied together. The UFO2 is actually a prequel to the UFO1 which means that the Earth has not been occupied yet and the planet Esperanza has not been even discovered yet.