Since I don't know the specific 'first Bengali detective story', it's hard to say exactly. But generally, it might have a local setting, perhaps in Bengal, with characters that are relatable to the Bengali audience.
The first Bengali science fiction is significant as it opened up a new genre in Bengali literature. It introduced Bengali readers to the world of scientific ideas and imaginative concepts. It inspired new generations of writers to explore the possibilities within this genre, and also helped in spreading scientific awareness in a more creative and engaging way.
I'm not sure which one is specifically the 'first Bengali detective story'. But some well - known Bengali detective stories might be a good start for you to explore the genre in Bengali literature.
To write a novel in Bengali, start by outlining your plot. Pay attention to character development and make them relatable. Also, familiarize yourself with the cultural and literary traditions of Bengali literature to give your work authenticity.