(Recap for 2Tidus! and other new players:
The Covenant forces are on Earth. No human presence was fortold yet the planet is inexplicably over run with them, looking for the Ark so they may bring Salvation to all. (Beginning of Halo 2). Their small force, not really expecting combat is under attack by the human marines as well as (inexplicably) the Flood (only way I can guess that the parasite is here is that it was already infesting one of the Covenant ships.) To make matters worse the Scarab has been destroyed by a Spartan (Demon) and another Spartan (Silent Wolf's character, (by the way, Silent Wolf, where are you and what are you doing?)) is closing on their position as they try to protect the Prophets (namely Assh, The Unforgiven's character)
Brent, reverently, "We will destroy all who imperil the Great Journey."