In 2001, humanity receives greetings from a highly advanced, peaceable Galactic Federation. However, all is not well, for a species of aggressive aliens known as the Posleen are attacking the Galactics. Since the Galactics are almost entirely unable to fight, they are appealing to the proven military abilities of humanity for aid.
However, things are rarely as simple as they seem, and humanity soon discovers that the Galactics are no friends at all. There are plots within plots, some going back to the dawn of humanity and beyond: plots that endanger the very survival of humanity.