From the introduction: Another world seeks a hero to help them. You will arrive here in the closing days of the 20th Century, on a world that is nearly identical to your own's history. However, strange lights have been seen in the skies, abductions and attacks are becoming commonplace. The world's governments have convened to create a new organization to fight this unknown enemy. This is the world of XCOM. Are you a bad enough dude to protect the Earth?