Oliver Richards writes action-adventure novels, and he wants to make Frank and Joe the stars of his next thriller. But he's unwittingly drawn them into a real-life tale of intrigue and danger. Thanks to him, the Assassins -- an infamous international gang of professional killers -- are back, and the Hardys are at the top of their hit list!

In their long and deadly war against the Assassins, the boys have always relied on the Gray Man, top operative in an ultrasecret government agency. But now he may have turned traitor, and they don't know whom to trust. One thing they know for sure: the terrorists are cold and ruthless...and their latest evil scheme could put seven million lives at risk!