Topshe turns Feluda in this hunt for a mysterious treasure that traverses Kolkata, traces a few steps back in Bangladesh and touches Darjeeling and Kurseong as well.

Saba from Bangladesh arrives at the Roychowdhurys in Kolkata with the story of a lost lineage - the story of her maternal grandfather. Queerly enough, a letter, very important but lost accidentally from the Roychowdhurys, traced its way back to the mansion, roughly simultaneously. The letter embeds a message via a deceptive riddle that hints at a mysterious treasure, hidden in a secret safe.