In a forgotten archive deep in the city, the young archivist Lin Mu lives a peaceful life isolated from the world and accompanied by ancient books. Until one day, while cleaning out a batch of dusty "miscellaneous items", he discovered an ancient key with a strange shape that was neither gold nor jade.
This key does not open a physical door, but leads to "echoes" - fragments of parallel time or potential future warnings that have been forgotten by history and erased by reality, but still leave their mark on specific places or objects. Lin Mu accidentally activated the key and was forced to be involved in the echoes of these fractures, experiencing key moments that could have happened, should have happened or never happened.
With the in-depth exploration of the echoes, Lin Mu discovered that these "silent echoes" did not appear randomly. They pointed to a huge imminent crisis and an ancient conspiracy hidden under the bustling modern city. At the same time, he also attracted the attention of a mysterious organization, who either wanted to harness the power of the echo, or wanted to destroy it completely.
Lin Mu must learn to control the key of time, interpret the secrets of echoes, and find truth and vitality in the fragments of time. Can he find the key to saving the world in the cracks of reality? Or is he himself the key echo?
This is a story about discovery, choice and struggle, where history and the future are intertwined, and reality and illusion are only separated by a thin line.
