Summary Calcutta, 1969. Byomkesh's son is selected to study Engineering at IIT Kharagpur. He leaves home after taking blessings from his parents. Ajit is busy with their publishing business. Satyavati feels that she now completely alone in the house. Ramakant (Vijayan V. Nair) is a cashier at a Kolkata bank. He lives in Kolkata alone, while he has family in Purulia. His landlord's name is Akshay Mandal (S.K. Das), who also has an account in the same bank where Ramakant works. Akshay lives on first floor and Ramakant is on ground floor. But Akshay has never invited Ramakant upstairs and always meets him only on ground floor.

12 months ago, Akshay left the house, locking his first floor, and instructing Ramakant that he can use the entire house if Akshay doesn't return in a week. The rent agreed is Rs 150/month for the whole house, as against Rs 50/month for the ground floor only. He requests Ramakant to keep depositing rent in his account. 3 days later there is a bad stench in the house & a dead body is found on the first floor. The body is of known smuggler and police issues a warrant for Akshay. Ramakant brings his family to Calcutta and starts using the whole house. He enjoyed the house with his family for 12 months.

2 months ago, a man saying that he is the brother of Akshay's wife (Anju), approaches Ramakant. He says that his sister (Akshay's wife) has been staying with him for many years, but now he can't pay for it and wants Ramakant to vacate the house. Ramakant refuses to vacate the house & gets a dog to guard his family, upon advice from the local police inspector. He also receives threatening anonymous letters asking him to vacate the house. Police gives Ramakant protection & he feels safe.

Now Ramakant wants to go on a month's vacation with his family & his friend (Debashish Majumdar) family. He is afraid that if he leaves the house, the woman claiming to be Akshay's wife will occupy the house. Debashish is also a clerk in the same bank as Ramakant. Byomkesh meets Debashish alone and finds that Ramakant is the one insisting on a month-long vacation & not Debashish. Byomkesh asks that Ramakant is a cashier and Debashish is a clerk. Cashiers earn twice as much as clerks. Yet, Ramakant always needs money, and Debashish is able to afford a month-long vacation with his meager resources. In Akshay's room, Byomkesh finds small iron boxes, big enough to store biscuits. Byomkesh advises Ramakant to leave for his vacation.

He then meets the police inspector and asks him to remove police protection from Akshay's house & instead arrange for secret surveillance of Akshay's house. The first night itself, they catch Akshay who was trying to retrieve some objects from the water tank at the top of the house. The objects were gold biscuits that were smuggled contraband. Akshay was a trader of illegal contraband. Akshay had killed the smuggler upon some dispute and then asked Ramakant to stay in the whole house, so that his hidden gold remained safe. He then tried to get the house vacated by various means & even paid Debashish to convince Ramakant to take a vacation.

Further investigation reveals 57 small iron cast boxes hidden in the water tank, each containing 2 gold biscuits. Each biscuit weighed 50 grams

• Adventure
• Crime
• Mystery
• Thriller