Byomkesh Bakshi

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.

Life at the mess-house takes a macabre turn when Ashwini-babu is found dead in his room, his throat slit and a blood-stained razor in his hand. Inspector Vidhubabu dismisses it as a "shut and open" suicide because the door was locked from the inside, but Byomkesh declares it cold-blooded murder. He notices oddities: Ashwini was a drunkard but the cut was surgically precise, and his shoes were caked in fresh mud. Byomkesh tracks the mud to a secret Chinese gambling den where Ashwini had been losing heavily. Dragging a terrified Ajit along in fake beards and mustaches, Byomkesh enters the den to find the missing link to the drug trade. Their cover is blown when Ajit’s mustache falls off, sparking a violent confrontation with the syndicate’s goons.

After a narrow, high-octane escape from the gambling den, Byomkesh reveals his true identity to a stunned Ajit. He explains that the mess-house itself is the epicenter of the drug nexus. Though Vidhubabu arrests Byomkesh on suspicion, the Commissioner intervenes, allowing the Satyanweshi to set a final trap. Suspecting Dr. Anukul is the mastermind, Byomkesh pretends to accept "medicine" from the doctor intended to silence him forever. In a tense midnight showdown, Byomkesh uses pillows to decoy his own murder, catching Dr. Anukul red-handed with a dagger. The "charitable" doctor is exposed as a ruthless drug lord who murdered the informer and then Ashwini for witnessing the crime.

Four years later, Byomkesh and Ajit are summoned to the opulent mansion of Karali Babu, a wealthy man found dead at his desk with a steel needle driven into his neck. The motive is clear: wealth. Karali Babu was constantly changing his will, pitilessly pitting his relatives—Motilal, Makhonlal, Phonibhushan, and the siblings Sukumar and Satyabati—against one another. While Vidhubabu focuses on the delinquent Motilal, who fled the house that night, Byomkesh looks deeper. He discovers chloroform marks on the victim and a missing needle from Satyabati’s sewing box. The tension rises as Satyabati, traumatized and beautiful, catches Byomkesh’s eye even as she becomes a person of interest.

The investigation into Sukumar, a medical student with the anatomical knowledge to kill with a needle, intensifies when Byomkesh finds a marked-up copy of Gray’s Anatomy in his room. However, the red pencil used to mark the murder method is missing. To clear the innocent, Byomkesh and Ajit venture into the city’s red-light district to track down Motilal. There, a woman named Dalim provides Motilal with a solid alibi, confirming he was unconscious from drinking during the murder. Vidhubabu remains convinced Sukumar is the killer after "finding" a new will and chloroform in his trunk, but Byomkesh suspects the evidence was planted. He meets a desperate Satyabati in secret, who confesses she saw a shadow she believed was her brother entering the room at midnight.

Byomkesh solves the mystery by timing the church bells against a witness’s testimony, proving the killer entered the room after Sukumar had returned home. The real culprit is revealed as Phonibhushan, the disabled nephew who felt like a "pity case" and sought to frame Sukumar out of resentment. Phani used the delinquent Makhan to obtain chloroform and stole Satyabati’s needle to commit the perfect crime, even marking Sukumar’s book with a red pencil found in his own possession. Realizing the game is up, Phani commits suicide by leaping from the roof, leaving behind a written confession.The season ends with Byomkesh, Ajit, and a new family member—Satyabati—sharing a meal until a frantic Habul arrives with a new case.