The Last Castle

For 700 years the Meks served without complaint; they were indispensable, for no gentleman would demean himself with toil. But now they turn against the strongholds of civilization—Castle Halcyon, then Sea Island, Morninglight, and Maraval—one by one the proud castles of Earth fall; last standing is Castle Hagedorn.
Winner Nebula Award 1966, Hugo award 1967.

Cover art by Todd Tennant