[2] It is an example of an alternate history novel in which a man from our reality becomes involved with another parallel world in which the American Revolution never happened and the secret of inter-world travel came under the control of the British Empire, which forged a unified Imperial world-state known as the Imperium.

Brion Bayard, an American diplomat on assignment in Stockholm, Sweden, is kidnapped by agents from a parallel universe.

The Maxoni-Cocini drive, invented by Italians Giulio Maxoni and Carlo Cocini at the end of the 19th century, enables traveling between parallel universes.

However, its development was extremely dangerous; almost all the time lines where it was attempted were destroyed, leaving a region known as the Blight.

This world, which was not believed to have the Maxoni-Cocini drive until it was determined to be the source of increasingly destructive raids, including the detonation of an atomic bomb, something the Imperium never developed (and does not fully understand).

Bayard the dictator is assassinated by the real conspirators, who are working for power-hungry factions in the Imperium itself, using stolen technology.

The collection A Century of Science Fiction contains a vignette by Laumer titled Worlds of the Imperium (Extract), which does not appear in the published novel.