Mitali was a worried mother. This time, once again, her 5 year old son Gogol had failed to pass the admission test in a reputed school. Mitali was determined to get her son admitted into a reputed school. Gogol loved the song of birds, the flight of the kites, the rustling of the leaves, the wide expanse of the blue sky.

Based on the novel Magno Mainak by Sharadindu Bandyopadhyay, the film portrays the iconic Bengali detective Byomkesh Bakshi along with his friend Ajit Bandyopadhyay as he investigates the murder of a Pakistani spy named Heena Mallick. He begins the investigation at the request of a political leader, Mr. Santosh Samaddar, who was a close friend of Heena's parents and had given her shelter after her parents' death. Will Byomkesh succeed?