The problem when dealing with terrorism, especially in a continent such as Europe, is about the borders between different nation-states and no interaction between the different countries and their police forces / specialized units. There are a number of issues that come to the fore when trying to get cooperation between the different nations involved, so the premise of the book is a bit difficult to believe; the book presumes that various countries agreed to contribute personnel to a security force that could go across nations and fight terrorist incidents where they occur (although in an admission of the need to get approval, the (Rainbow Six - the name of the security force) needs to be called in by the nation involved).
Also, the incidents of terrorism that happen nowadays are not the bank robberies or kidnapping in high-profile incidents, but cases of bomb blasts and the like, where you either need a security force to prevent such incidents from happening, or a good investigating agency to go across borders and determine who actually carried out the incidents. However, if you leave these quibbles aside, the book presents the action of the acts of terrorism (including the reaction of this specialized force - Rainbow Six - which is headed by John Clark, he being the one who had proposed the formation of such a force to the President, one assumes that was Jack Ryan).
Tom Clancy was never fond of the environmental movement, and that comes out in several of his books, although this book takes the narrative much further, presenting a plan by some rabid environmentalists to create a bioweapon that would be launched during the Olympics, and would kill of most of the people currently present on earth (a few would remain who would either have natural immunity, or who were given the antidote). When Clark learns about his, what does he do ?