Hahaha! Over at informationweek.com they describe the halo plot as follows :
"Halo 3 is a so-called first person shooter featuring Master Chief, a biologically enhanced super-soldier who has to blast his way through a futuristic, 3-D landscape to survive and accomplish missions. He's countered at every turn by a shadowy terrorist group called The Covenant."
Do your homework!
Good job to halo 3 for $170 million in sales on its first day!