Sell-Swords of Mars

The heroes are mercenaries, seeking work among the lesser independent cities of Mars. When an attack dams up the only canal of the city of Pi-Ramesh, the city's young Queen hires these Sell-Swords of Mars to come to her aid as the city's lifeblood dries up. Can the heroes stop the onslaught of a seemingly unstoppable enemy, and save the weakened city?