Joe Hardy's girlfriend is killed in a car bombing and the Hardy boys search for the people responsible. Frank and Joe are captured by the Gray Man, an agent for a top secret government agency, called the Network, that desperately wants the Hardys under wraps for their own good.

They then learn that Iola's killers are an infamous international terrorist group known only as "The Assassins".

After a trip to London, the alleged headquarters of The Assassins, and a run-in with two members of the organization, the Hardy's return home to Bayport, where they discover the horrible truth - the car bomb was just a warm up and The Assassins have an even bigger target in mind, the Bayport Mall and presidential candidate Philip Walker.

With help from Tony Prito, Callie Shaw, and Iola's brother Chet, the Hardy brothers search the mall the bomb, that they know The Assassins have planted there. Before they can locate it however they are captured by Iola's killer Al-Rousasa, who ties them up and locks them in the basement of the mall, along with the bomb, which is set to go off the following morning when senator Walker is giving his speech.

They manage to get free and Frank disarms, then they go to the upper levels of the mall, to look for Al-Rousasa. Joe is looking on the top floor when he sees him, pointing a gun at Philip Walker, who is giving his speech. Joe attacks him before he can shoot, and a fight ensues. Al-Rousasa ends up falling off the balcony, Joe tries to catch him but he slips, but he slips out of his bloodied hand, and Al-Rousasa falls four floors to his death. Joe remembers what he was told earlier in the case.