One day, Tang Xiaotian was sitting glumly on a train. As for why he was so gloomy, it was because he was tasked with investigating an unknown killer.
And why was Tang Xiaotian on this train in the first place? Because the killer might well be on board.
Actually, all of this went back to Yusaku Kudo, or else Xiaotian would never have ended up on this train.
Chapter 634