This action-oriented suspense thriller traces the complex sequence of events that unfold when renowned Bengali private investigator Pradosh C. Mitter (Feluda) is hired by wealthy businessman, Dinnanath Lahiri.
During a train journey Dinnanath Lahiri's suitcase got accidentally switched with someone else's, and he hires Feluda to locate it and bring it back to him, especially because the suitcase contained a valuable manuscript written by Shambucharan Bose.
The case takes Feluda, Topshe and Jatayu to Shimla, where they discover a priceless diamond in a film container, disguised as a betel-nut. 'The Three Musketeers' face great danger in Shimla from all directions. Will the investigators succeed in solving the case?