In the distant future, humanity has floundered among the stars for almost a million years. With Earth forgotten, and the secrets of nature decoded, only one great unknown remains: Who were the Big Sisters? On countless worlds we find their ornate ruins and impossible technologies: universe factories, time-travelling mountains, and dictionaries of the exactly-right-words. Who created these things and why? Surely they were a cousin of humanity, some long-forgotten offshoot of our species. Yet their absence is as much a mystery as the miracles they left behind. From the collapsing halls of the galactic social engineers, to the nebula laboratories of the cosmic whales, Sublimia Syndrome is the story of five seekers, separated by millennia, desperate to reconcile with the once-great true adults.