This is a world where doppelgängers are rampant. Yu Tang has become a noble night-shift security guard whose duty is to stay inside the security post to identify doppelgängers, notify the corresponding organization for handling, and ensure that no doppelgängers sneak into the residential area at night. However, this job is not easy to do. Here, what he faces seems to be more than just doppelgängers.