The Midnight Anonymous Letter

Three bizarre murders occur in succession in Jiangcheng: a retired professor dies in a study locked from the inside, with only half a cup of tea left to cool at the scene; an online celebrity suddenly suffocates while livestreaming, and the camera catches only a glimpse of a black-gloved hand; an architectural designer is found collapsed on the rooftop of a newly completed skyscraper, with seven shards of porcelain scattered beside him.