Planchette

The story starts with Aakash & Rukmini talking about their maths exam, which both of them didn't gave very well and entering the library were Shouvick & Nandini was waiting for them. To discuss about the planchette, Shouvick was holding a book in which they all get to know more about it, after reading the book the 4 student student understood that it is a life-risking task with full of danger. Then Aakash Told everyone that only Sahil Kumar there Commerce teacher is an expert in planchette, but they all have to go and ask him about it. So everyone decided to go and ask Sahil, everyone else also agreed during the break-time all 4 went to the staff room and found Sahil all alone having his tiffin. It was Rukmini who asked Sahil, first he denied but later on he agreed to help them. Sahil called-up Nandini and told to reach his house at 6 pm. But Sahil told other 3 student to reach his house at 7:30 pm.
So everything was going well until, Nandini reached Sahil's house with all the stuff required for the planchette. Sahil used to have lustful feelings towards Nandini & tried to rape her but in that process Nandini got killed accidentally by Sahil. Sahil quickly hide her body in his basement. Then after sometimes everyone arrived at Sahil's house and Sahil gave them some snacks and juice to have, told them Nandini won't be able to come.
After sometime they start the planchette and called a random spirit which possessed Sahil, because he was the medium between the spirit and real world. then Aakash Asked the spirit who is he/she the spirit answered her name is Nandita, Shouvick & Rukmini asked that how she got killed the spirit told them she was raped by her school teacher. Rukmini asked what was the name of the murderer , hearing this question the spirit kills Sahil brutally.
The Trio called-up the cops and they came to know that Nandini was raped by Sahil which was proved by the forensic report. Thus they understood that it was Nandini Who killed Sahil .