Sustenance is a story of a small group of Earth colonists held in virtual slavery on an earth-sized moon orbiting around a large planet. The colonist are forced to mine a valuable ore, denzinite, necessary for the construction of starships. The miners are assisted by indigenous people, humanoids called Dagi, to help mine the denzinite. A cargo ship comes regularly to collect the ore and bring minimal supplies to the miners. The moon is arid and without oceans or rivers, so the colonists must rely on SolVesCo's high tech water collectors/dispensers and the regular supplies for survival.
Due to an unknown catastrophe back in the Solar system, the SolVesCo cargo ship is late and supplies are rationed drastically. Finally the water dispensers stop providing water. Carl Maxim a young miner, tries to find out why the supplies have stopped but is unsuccessful. After several weeks, Carl, exhausted and dehydrated, collapses and is taken underground to the home of his Dagi friend. The Dagi reveal they have the answers to the miners' problems.