Imperium — Keith Laumer

There are Millions of Parallel Worlds--and Most of Them are No Longer Inhabitable. The World That is Home to the Imperium is Desperately Fighting Not to Join Their Number!

Brion Bayard had been an American diplomat--until he was abducted on the streets of Stockholm, and thrust into what he thought was a truck. At first, he was relieved to find that his abductors were very apologetic, and very British. Then they began speaking about nations and leaders which Bayard had never heard of. That was understandable, they told him, because they were from Earth, but not his Earth.

There are millions or more parallel Earths, each different in some slight way from the other, where history has taken every possible turn--where the heirs of Napoleon rule Europe, where King John tore the Magna Carta to shreds and executed those who had presented him with it, even one where the ancestors of homo sapiens lost the evolutionary struggle to another upright ape, who became the dominant intelligent lifeform. But mostly there are uninhabitable worlds, destroyed by the discovery of the technology to travel from one parallel Earth to another and the misuse of it.

The Earth of the Imperium was at war with another parallel Earth and Bayard could stop the war by killing the ruler of the aggressor Earth and replacing him--because the ruler was a parallel version of Bayard. But when Bayard went on his mission to the alternate Earth, things didn't turn out to be quite that simple. . . .

And that was only the beginning of Bayard's adventures as he defended his new homeworld, both from internal enemies and invaders from the other side of time, becoming the staunchest and most resourceful defender of the Imperium!