Summary Calcutta, 1955. Miss Madhubala Rai (Madhu Mohan) meets Byomkesh (Rajit Kapoor) & Ajit (K.K. Raina). She was a nurse in Patna Medical College, but now lives in Calcutta, with her boy Prabhat (Rakesh Sahu) whom she adopted. A pregnant woman was admitted in Patna 20 years ago. She died in childbirth, and no one came to claim the baby, so Madhubala adopted him. When the boy was 5 years old, Madhubala received a letter with Rs 400 that said that the man knew that his boy was with Madhubala and should continue to be so.

2 years ago, Prabhat started working with Anadi Babu (Sadhu Meher), who is impressed with him & wants to adopt him. Anadi convinces Madhubala to stay with him as well. Anadi had an elder brother, who died, with 2 sons, Nimai (Loveraj Kambli) and Nitai (Kush Kambli). Both are goons and hunters. They have shifted base to Calcutta & Madhubala fears they want Prabhat out of the way to take control of Anadi's property. Byomkesh goes to meet Anadi, under the guise of renting property, but Anadi flatly and rudely refuses him and Ajit.

Keshto is Anadi's old friend, who is now destitute and lives with Anadi, along with Prabhat and Madhubala. On Diwali night Keshto has a big fight with Anadi as he won't give money for drinks & storms off. He returns at 1 am to find Anadi dead in his balcony & Prabhat and Madhubala blaming him.

According to Prabhat, Nepa (Ashok Mishra) (Anadi's secy) left the house at 8 pm, Prabat & Madhubala left at 8 30 pm. Prabhat dropped Madhubala at the cinema at 8 45pm, went to his shop to do work, picked his mother at 11 45 pm and then came back home together.

Looking at Anadi's books, Byomkesh finds that he had loaned Rs 5000 to Dayal Hari Majumdar (Pravin Kedia) 1 month ago. Prabhat wanted to marry the daughter of Dayal, but Anadi was not in favor. Also, Nimayi and Nitayi arrive with their lawyer for their uncle's property. The lawyer Kaminikant (Avinash Masurekar) tells Byomkesh that Anadi never adopted Prabhat legally and thus has no rights to Anadi's property. Byomkesh confronts the lawyer about his knowledge of Anadi's death, since it has not even been 2 hours. But Nimai interjects that Anadi has been dead for several hours, which means he knew when Anadi died.

There is a hotel opposite Anadi's house. Byomkesh finds the key to Anadi's locker in the street directly below one of the hotel room windows. Byomkesh investigates and finds that the owner of the hotel (Somesh Agarwal) had rented that room to 7 boys. 2 had returned home for holidays, 2 had gone to city for Diwali & 3 were playing cards with the owner till 10 30 pm. They slept at 10 30pm. One of the boys (who went to city) returned at 12 midnight and the other hadn't returned yet.

Another room on 3rd floor is rented to Nityanand Ghoshal, who doesn't stay in the room, but comes and goes frequently. He came to the room at 10 pm. He has rented the room for the last 6 months. He always had a longish bag in his hands. He returned at 11 pm. Byomkesh finds that the window of Nityanand's room opens into the balcony of Anadi's house. He also finds a bullet lodged in Nityanand's wall.

• Adventure
• Crime
• Mystery
• Thriller