Xenonauts-2 is a large and complex strategy game loosely inspired by the classic X-Com games from the 90s. It is not a direct sequel to the first Xenonauts but rather an updated and improved portrayal of similar events. The time period of the game is no longer the 1970s but instead the modern day, however the action now takes place in an alternate history where the Soviet Union never collapsed and the Cold War never ended - you can thank extraterrestrial interference in human politics for all of this!
The Xenonauts have already existed for decades when the game begins, having been formed as a joint NATO-Soviet organisation to secretly study the fragments of a crashed extraterrestrial craft found in Iceland (the discovery of which nearly sparked a nuclear war until the Americans agreed to share it). Unfortunately, little useful knowledge is gained from the remains and the Xenonauts fade into irrelevance as time passes - despite having circumstantial evidence that the aliens are continuing to visit our world, they are unable to prove it.
The game begins when the aliens begin an open invasion of Earth. Half a dozen hostile UFOs appear in our skies, attacking several major cities. The various world powers attempt to defend themselves in vain, unable to track the UFOs and suffering heavy losses on the few occasions their fighters manage to find their targets. When the UFOs retreat after a day of sowing terror, both superpowers agree a united global front against the aliens is needed - as long as the other isn't in charge of it.
Despite being an intelligence / research organisation, the Xenonauts are chosen as the compromise candidates to co-ordinate the defence of Earth. The Commander is the only military officer sufficiently highly regarded by both sides to be an acceptable candidate for leadership of the organisation, and is put in charge of assembling a "first response" force capable of operating anywhere in the world. The price of their support is that any research acquired by the Xenonauts be shared with the funding nations.
The game therefore begins with the player taking charge of a small organisation and having to quickly grow it into something capable of defending the planet. The aliens, meanwhile, are broadcasting messages promising that any who surrender will be spared. Humanity begins the game united behind the Xenonauts, but failure to effectively defend their territory will lead entire regions of the world to conclude that they are better off taking their chances with the aliens!
Finally - a few familiar faces are returning in the alien and Xenonaut ranks, but remember that nothing from the first Xenonauts is considered canon for the sequel!