The communication between MESA-7 and the Military have been cut off. You, Frank and rest of your squad (Bravo Team) have been sent in to figure out why MESA-7 got into deep silence. While you fight for the answer the Russian Corp "Vlad Corp" enter room, they thought the reason of the "monsters" was because of MESA-7. While MESA-7 was doing "The Cure" the Black-Ops stole it and claimed it as their own. While you fought inside the facility the Vlad Corp planted a nuclear bomb to exterminate all threat in the area. But they didn't know a city was near the complex, so the little disaster went bigger.
Working also on a Coop Version ;P