Seeds of crime, ploys of destruction, and legends of a hidden treasure lurk in an erstwhile royal fort of Jankigarh. Shotyaneshi Byomkesh Bakshi returns, along with Ajit and Satyabati, to unravel the mysteries in the dark hallways of the mysterious fortress.

Swarnaja (Koel Mallick) is a hard-working do-gooder radio jockey with the rarest blood group in the world, Rh null blood group. She has been brought up by her grandmother. Her four year old son Pawrag is kidnapped by Shammo, an imposter.

As Byomkesh Bakshi tries to solve a murder mystery, a myth of a buried treasure at the fort surfaces following a bizarre series of deaths. How does BB demystify the case? Adaptation of the adventure detective novel written in 1952 by Sharadindu Bandyopadhyay.