This story is set in the near future. Some terrorist organization sponsored by yet another organization developed a system of portals that let you move almost any object anywhere in the world. This provided an opportunity for terrorists to move fighters right under the noses of the authorities. Besides fighters they use robots with nuclear warheads, which provides them the a "parallel organization." They have already set up under more than a dozen cities, but scientists have found portals that have "interchange" points, very long distances, which do not work completely, and so there are places where the terrorists have to translate their robots from one portal to another. Exploration calculates these places, and your goal is to establish defenses at these points and destroy all robots. Fortunately, they are highly combustible. The ultimate goal is to identify the enemy's headquarters, and destroy it.