The story so far..

Call of duty modern warfare 3 is to be the next release in the Call of duty series. The plot line follows Modern warfare 2 and starts where it left off, the Russian federation continuing their invasion of the
 United states and certain areas of Europe. Campaign stages are also planned for Somalia, Sierra leone, Moscow and Dubai taking this game to a truly global scale.

Incase you havn't see it, here is the official MW3 gameplay trailer.