The trio of Feluda, Jatayu, and Tapesh have been invited to Panihati to investigate the case of Jahangir's missing gold coin. The client, Shankar Prasad Mitra, had a collection of 12 gold coins but on his last birthday, one of them was stolen by one of his most trusted invites. He invites the same group this year and asks Feluda to catch the culprit while hiding his true identity.
Ambar Sen, a Bengali comes to Feluda and informs him that he has got threatening mail. Later Mr. Sen is kidnapped. Feluda investigates.
An old man from Ghurghutia village near Palashi invited Feluda to solve a puzzle. The man's pet parrot recites a numeric code which is actually the combination number of his iron chest. The parrot says— Trinayan, o trinayan, ektu jiron. When Feluda solved the puzzle, he gave him four rare books of Émile Gaboriau as a reward. The very next day when Feluda returns to Kolkata with Topshe, something fishy smells in the old man's house. He started the last time investigation and it revealed that it was all a made-up plan and there was a murder behind the entire plot.
While at a felicitation ceremony, Feluda, a detective, meets Joychand, a simple man who owns a pink diamond. When several buyers set their eyes on the precious stone, Feluda must save the day.
