Kolkata, 1964. The city’s underbelly is gripped by a lethal heroin trade. When a drug delivery in Chinatown ends in a brutal alleyway murder, the Home Minister demands immediate results from a failing police force. Enter Byomkesh Bakshi, the "Satyanweshi," who goes undercover as Atul Mitra to infiltrate the heart of the conspiracy. Disguised and observant, he arrives at a local mess-house run by the charitable Ayurvedic practitioner, Dr. Anukul Hazra. Here, he meets Ajit Bandyopadhyay, an aspiring thriller writer who unwittingly becomes the roommate of a man seeking a truth far more dangerous than fiction. Byomkesh immediately begins weaving himself into the lives of the mess residents, saving a young student from police harassment while keeping a sharp eye on a suspicious post office clerk named Ashwini.