Force fields have been a staple of science fiction for at least sixty years. It takes a brilliant author to take an old concept and use it in a fresh, creative way. And that's just what Vinge has done here.
His characters have invented "bobbles". These are spherical force fields that can be generated some distance from the generator, hence the generator itself is not "trapped". Nothing can get in or out of a bobble, although the mass an inertia of the object(s) enclosed are preserved. So bobbles can be pushed, transported (if small enough), and sometimes even float. Objects "embobbled" are more or less effectively ejected from the universe. If one knows how to generate and aim them, therefore, they make terrific offensive weapons. You can bobble up your enemies, and they're gone! You can bobble up an exploding nuclear device, and it's harmless!
At the beginning of the story, it is thought that:(1) bobbles are permanent, and (2) people inside bobbles must have suffocated by now, since no air can get in or out, hence bobbles are deadly weapons as well as effective ones. Both assertions turn out to be wrong. We discover fairly quickly that bobbles "pop" in time, and that time stops for everything inside a bobble. Only one group, the Peace Authority, has the knowledge and resources to generate bobbles, and hence, they rule the world. As the story opens, they are learning about those misunderstandings.
Moreover, soon they are not the only ones who know how to make bobbles. A defector from their ranks, who has been opposing them "underground" for decades discovers a malnourished Hispanic boy who is an undeveloped genius. The defector, Paul, quickly develops the boy, and between them, they create a low-power, portable bobble generator. They are helped in their plans by a female shuttle astronaut, who was one of the first bobble victims. They are opposed by the deadly Peace Authority cop, Della Lu.
Along the way, Vinge paints an excellent picture of the culture that develops during this time. He also realistically depicts what computers can and cannot (or will and will not) do. It is a fine story which demands a sequel. Fortuately, there is one: Marooned in Realtime.