In the bustling city of Culcutta during World War II, Byomkesh Bakshy (Sushant Singh Rajput), a self-assured, collegiate is approached by his classmate Ajit Bandopadhyay (Anand Tiwari) to find his missing father. To get a better understanding of the case, Byomkesh decides to stay into the boarding house where Ajit's missing father used to reside. The house was run by Dr. Anukul Guha who administers free health care for the poor. While on his hunt he unintentionally staggers upon a dark secret. The mysterious plot unfolds when Byomkesh tries to solve the case piece by piece and while doing so touches the most unexpected cards.

After an unexpected twist, Byomkesh gets a better grip of the case and as he digs further, the whole new mystery of a dangerous gang unfolds. The drug scenario, the brutal bloodshed and several other pieces is the evidence of the violent situation of the war torn era. Where will this case lead him to, is the further watch in the film.