Silver Jiken: Case #4.5 - Face

Applying to join the Administrative Inspection Office, Sakura Natsume, the protagonist, embarks upon six months of training. As part of her training programme, Sakura is tasked with writing reports about unusual crimes. During this process, she interviews Sumio Kodai, a former detective who is now being held in police custody after committing a crime of conscience. "If you don't connect with the darkness inside yourself you can't understand criminals, and you can't become an investigator." Sakura is left shaken by Sumio's words. And then, one day, news about a serial murder case is sprung upon her...

(Source: ASCII Corporation, translated)

Silver Jiken: Case #4.5 - Face is a spin-off novel of the 1999 visual novel Silver Jikan (シルバー事件) and takes place within the game's timeframe.