Gate of Ivrel (Electronic book text)

Scattered about the galaxy were the time-space Gates of a vanished but not forgotten alien race. In their time, long before the rise of the native civilizations, they had terrorized a hundred worlds -- not from villainy but from folly, from tampering with the strands that held a universe together.
Now the task was to uproot these Gates, destroy their potency for mischief, take horror out of the hands of the few who hungered for power by misuse of the Gates.
This is the story of one such Gate and one such world.