Theory:

The lesson "Expert Detectives" is written by Sharada Dwivedi. It follows Maya's and Nishad's quest into unravelling the mystery behind Mr Nath's identity.
 
The lesson is unique for its ending. Unlike the traditional stories where a resolution is provided at the end, "Expert Detectives" has an unconventional open-ending.
 
The ending is unconventional because several significant questions in the lesson are left unanswered. The primary quest of the lesson was to discover the identity of Mr Nath. The entire lesson is built on the question, "Was Mr Nath a crook or not?". Nevertheless, it remained unanswered till the end.
 
Moreover, there are also other questions as to what would happen to the investigation. For instance, the lesson ends with Nishad walking out of the room, leaving Maya with her sheet of facts. As a result, the progress of the investigation is left uncertain. This uncertainty gives rise to several other questions: will the investigation continue? Will the siblings find common ground where they could work together again? Will they be able to work objectively without mixing their personal preferences into their investigation?
 
With so many questions left unanswered, the story becomes open-ended. It is for the readers to speculate, analyse, interpret, and arrive at the desired conclusion.