50 Cent and G-Unit put on a sold-out performance somewhere in a fictional Middle Eastern setting, but instead of payment, the concert promoter offers him a diamond-encrusted skull that's valuable to this particular war-torn country.
As they're about to leave the country, they're ambushed and the skull is taken. Throughout the game, 50's trying to track these people down and find out who they are and why he was ambushed.
We drew inspiration from the movie 'Three Kings.' [source]
Honestly? The game doesn't seem any more ridiculous than Hammerman and its magical, anthropomorphic dancing shoes.