In an Arizona canyon, a UFO crashes releasing anthrax spores. There are a number of innocent victims left in its wake. On the side of the object, a Nazi Swastika is discovered. The authorities wonder if this might be part of a plot of home grown terrorists or could it be part of a nefarious plan hatched by the Nazis over a half century ago? Lewis Sharp, an expert in World War II weapons, and in particular biochemical weapons, is brought into the investigation. He becomes convinced that indeed it is the real McCoy and he warns that there are two more devices somewhere on the planet scheduled to be detonated in the very near future.
Those behind the plot have left a cryptic note hinting at another attack. Now Sharp and his colleagues set off on an international adventure to discover who is behind the plot, their purpose for doing so, the timeline for the next attack, and all the while trying to convince the Executive Branch that the threat is real and could lead the world to the brink of another world war. And, in one of Napier's trademark ploys, they have five days in which to solve the problem.
As a writer of fiction, it is my opinion that Napier is not in the same class as Asimov was. While the story is interesting, there are portions that have the reader looking for precedents or some raison d'etre for whatever.