The Key of Time: the Stopped Hand

Six months before his death, Gu Mingshan completely cut off all contact with the outside world, claiming that he wanted to produce "the most important work in his life", but this work disappeared out of thin air after the incident. The murderer's methods were extremely professional - the incubation period for thallium poisoning lasted for weeks, which meant the murderer had a strong alibi. What's even weirder is that a handmade pocket watch was found among Gu Mingshan's relics. A line of small words was engraved on the back of the dial: "Time will tell the truth, but the truth requires a key." And everyone related to Gu Mingshan seems to be guarding a time-related secret.