[6] The film, which is based on the fictional detective Byomkesh Bakshi, stars Sushant Singh Rajput, alongside Anand Tiwari, Neeraj Kabi, Swastika Mukherjee and Meiyang Chang.
In November 1942, shortly after the Japanese take over Burma, a group of Chinese men from the Green Gang are unloading opium in Calcutta.
The following day, Byomkesh visits the lodging house Bhuvan resided in, headed by Dr. Anukul Guha, and takes a room to investigate.
Byomkesh and Dr. Guha return to the factory and find Bhuvan's body in a machine, causing Deputy Commissioner Wilkie to question Sikdaar.
Dr. Guha leaves Calcutta temporarily, but sends Byomkesh a stamp, confirming he had faked the letters and killed Bhuvan.
Returning to their room, Ajit vents about his father, revealing Bhuvan had lost his job at Hind Chemicals when they learned his master formula contained opium and addicted customers.
Realising Ashwini is addicted to Bhuvan's custom paan blend, Byomkesh takes a chew and euphorically creates a mural of his understanding of the entire case, revealing Sikdaar said the words Young Gun to him before dying.
Byomkesh requests Dr. Guha, Satyavati, Sukumar and Dr. Watanabe to meet him at the lodge, pretending to have joined them and claiming they have been betrayed.
At the lodge, Byomkesh reveals Dr. Guha is Yang Guang, conned the idealistic Sukumar into his deal, and plans to make Calcutta as the drug capital of the world.
The air raid sirens are set off; using this, Byomkesh convinces Watanabe to leave and stop the attack to save his men.
[10] In July 2013, Dibakar Banerjee revealed that YRF had bought the rights of "31 of Byomkesh novels in all languages outside Bangla".
[15] After Khosla Ka Ghosla, Dibakar Banerjee wanted to make this film and he approached Aamir Khan to play the antagonist.
[18] Earlier reports suggested that fashion designer Sabyasachi's assistant, Divya Menon, would be making her debut as an actress in this film as Rajput's character's wife.
The full song of "Bach Ke Bakshy" was published in a music video featuring Sushant, dancing in a parking lot, on 16 March 2015 in the official YRF YouTube channel.
[30] Banerjee says he changed the 'i' at the end of the protagonist's surname Bakshi to 'y' for "typographical balance", stating that the 'i' felt "too thin" and that 'y' was a "stronger alphabet".
An apparel line titled NOIR 43 was launched at the Amazon India Fashion Week (AIFW), New Delhi, on 26 March.
[39] Prior to release, Banerjee expressed interest in creating a franchise based around Byomkesh Bakshy, if the first film performed well.
[44][45] Banerjee said that Byomkesh's adventures would continue with the upcoming installments exploring his relationship with Ajit, Satyawati and his nemesis.
[48][49] Rohit Vats of Hindustan Times gave 4/5 stars and wrote "It’s a film that will keep you glued to the screen for all the 135 minutes it runs into.
"[50] Surabhi Redkar of Koimoi gave 4/5 stars and wrote "Detective Byomkesh Bakshy is a delicious thriller filled with elements that make you rack your brains too.
"[52] Kusumita Das from Deccan Chronicle gave 3.5/5 stars and wrote "There are two kinds of audiences for this film --- those who know Byomkesh and those who don’t.
"[53] Srijana Mitra Das of The Times of India gave 3.5/5 stars and wrote "A chilling climax masterfully ties up the tale - but 30 minutes less would've given this detective a much tighter grip.
"[54] Shubhra Gupta of The Indian Express gave 3/5 stars and wrote "Detective Byomkesh Bakshy's biggest weakness is its leading man: Sushant Singh Rajput.
"[55] IBN Live gave 3/5 stars and wrote "In the end the film has a lot going for it, even if it isn't as fully satisfying as Banerjee's previous works.