A 7-year-old apartment building located a 7-minute walk from the station, close to the city center and equipped with furniture and appliances for convenient living. A man working for the company managing this popular property gets his hands on the master key, normally kept securely locked away, and begins maliciously invading the rooms of female tenants. The first target is an estimated 23-year-old woman dressed like an office lady, who has just returned home from a new employee welcome party. Seemingly drunk, she cheerfully chats on the phone with her mother, but suddenly feels nauseous and abruptly hangs up. She tries to rinse her mouth with tampered water, intending to soothe her throat, but collapses in the bathroom after vomiting gastric fluid and quickly loses consciousness.