Northworld — David Drake

WORLDS AT WAR
The Consensus ruled twelve hundred worlds--but not Northworld. Three fleets had been dispatched to probe the enigma of Northworld. None returned.

Now, Commissioner Nils Hansen must face the challenge of this distant planet ... a gateway to nine alternate worlds. There, he will confront a world at war, a world of androids, a world of sentient machines ...all unique, all lethal.

But deadliest of all are the men who would be gods. Who rule these worlds with absolute power. And who challenge all trespassers ...Like Commissioner Hansen.