In the far future, the earth is reduced to an ocean planet with a single small island upon which reside the Lustrous, person-shaped living gems who are essentially immortal.
While most of the 30-odd gems are content to live together and repeat their same tasks for hundreds or thousands of years, Cinnabar is different.
Because of the dangerous metallic mercury it exudes, it has chosen the night watch, an unnecessary, lonely, bitter work that only it can perform.