The world of Alienoïds is the same we live in, with a small difference: aliens have been on earth since 1938, plotting, infiltrating governments and preparing for their final goal, a planetary armageddon which will allow them to harvest the entire population of the planet and fill the freezers of their living mothership with tasty carbon-based lifeforms.
The players' characters are alienoïds, extraterrestrial infiltrators tasked with protecting the alien master plan against the human resistance and other alien species. They'll have to adapt to and understand human culture and technology (which don't make any sense to a galactic predator using biomechanical technology), and manage the complexities of human emotions (the longer they are exposed to humans, the harder it is for their empathic brains to avoid being tainted by feelings and heretical thoughts like compassion or fear).
The game system uses several d6: actions are resolved by rolling a number of dice equal to the sum of a stat and a skill, each result of 5 or 6 is a success. The number of successes allows the gamemaster to quantify the result. There are also rules for playing diceless.
The book includes the rules system, a detailed chronology of the world since 1938 (the year of the alienoïds' first contact with earth authorities), details about the alien master plan and those who oppose it, a huge list of biomechanic gear (from weapons like blasters and flamethrowers - which need to be fed regularly and fart a lot, to spaceships and backpacks), and a seven scenarios campaign, starting with the characters' first assignment on earth and ending with the characters, now overwhelmed by human feelings and emotions joining the Resistance and taking the fight to their own specie.