The Paradise Game, by Brian Stableford - 4th in the "Grainger/Hooded Swan" series. When the Hooded Swan landed on Pharos, it was all a paradise could be. They came to investigate, but stayed to protect. Unless they played the role of the angel with the flaming sword, very soon this softest and gentlest of all men's dreams would become another gaudy hellhole of exploitation. But this world had a serpent of its own.