How did the masked restaurant Xintian discover the mountain shore?

Shanan was drunk and told the secret. According to the movie plot of "Masked Hotel", Xintian was appointed by the police to sneak into the hotel and turned into the front desk to secretly investigate the murderer. However, when drinking one day, Yamanaka was drunk and told the secret, and Xintian discovered Yamanaka's identity as a policeman. Masked Hotel is a film based on Keigo Higashino's novel of the same name. Directed by Masayuki Suzuki, written by Okada Daoshang, starring Kimura Takuya and starring Masami Nagasawa.