Bakso Rahashya (English title : Incident on the Kalka Mail)[1] is a Bengali novel by Satyajit Ray featuring the private detective Feluda.

During this time, Feluda meets with Pakrashi and learns about the other two men in the train compartment i.e., Dhameeja and Kedia.

After some aimless conversation, Lalmohan Babu hears everything about Feluda's new case and also about his prospective tour to Shimla.

While looking for Mr. Puri's house, the duo are attacked by two muscular thugs who tackle Feluda and Topshe to the ground, snatch the briefcase and flee from there.

That night, while Feluda and Topshe are planning to go to bed, Pakrashi arrives to meet with them; he demands that Feluda should hand over the manuscript to him which was in Lahiri's briefcase (there was a valuable manuscript inside Lahiri's briefcase, titled A Bengalee In Lamaland written by Bengali explorer and author Shambhu Charan Bose) and he offers money for it.

While Topshe and Lalmohan Babu go out for a tour around the city, an unknown man arrives in their hotel, meets with Feluda, knocks him unconscious and steals the briefcase.

That evening, while on their way to Shimla by train, the trio discover a diamond stuck inside a Kodak film roll container which they had during this entire time.

Feluda now understands that the thugs are actually trying to steal the Kodak film roll container because of the diamond.

After the Lahiris discovered Shambhu Charan's box in their house, Prabeer found the diamond and planned to earn money by selling it.

When Feluda starts describing the punishment that he'll face, Prabeer tries to escape, only to be knocked out by Lalmohan Babu when he hurls his boomerang at him.

He also reveals that he stole Shambhu Charan's manuscript from Lahiri's briefcase in the Kalka Mail and was copying it, intending to publish it and become famous.