In the New Calendar era in the near future, human civilization has spread all over the solar system, but they have no idea that they are living in the "petri dish" of the universe. There is an ancient mechanism called the "immune system" deep in the universe. Like a gardener pruning a garden, it regularly "harvests" civilizations that develop too quickly to prevent "infection" - that is, the system collapse caused by civilization's understanding of the truth of the universe.
Lin Su, a 28-year-old Deep Space navigator, suffers from a rare time perception disorder and can hear "echoes of time." During a routine wormhole jumping mission, he unexpectedly encountered a "black entity" - a reconnaissance unit of the immune system. This contact triggered the secret lurking deep in his genes: he was not a natural human being, but a carrier of the consciousness fragments of "Observer-7", a "key" created by ancient civilizations to combat the immune system.
