On March 7, her sister Cheng Yu disappeared mysteriously on her way out to order a cake for her sister Cheng Ran. After calling the police, no such person was found. Overnight, except for Cheng Ran and her good sister Qin Xia, almost no one remembered Cheng Yu, as if she did not exist. In an accident, they came to a place called Base No. 7. One puzzle after another was thrown to them, and the truth emerged one after another.
Intention: None