Sara or Sunaina?

Byomkesh Bakshi.

Soon after his first case, he goes to Spain to celebrate his success. He was still in dilemma where is Sara. He meets a girl named Sunaina and soon after they get close and marry each other. 

Both of them come back and start afresh. He notices a strange thing about Sunaina, his wife. Whenever he hears about a case to be resolved, somehow his wife always gives an idea. He starts thinking to be his good luck charm. 

Once she went to her parents home. Since she wasn't there Byomkesh tries to solve the case but he couldn't. He took her photo still he didn't get the plot in his mind. Then he goes to his room and checks his almirah. He finds a strange kind of a slate kept there. When he put little fire below it started to imprint some words. And he got the case mystery solved. 

Now he realised how he could do it. It wasn't the skill but the trick of the slate. He wrote some question and it was solved with answer visible with fire below it. Thereafter he used to solve any case with just the slate. 

When his wife came back he asked her about it. She got scared. She started crying. She told Byomkesh that she is Sara whom the world is looking for killing Dr. Owen. She stole this slate from him when he became inhumane. And then she changed her name. He understood the whole story and forgave her. They both loved happily thereafter.