Associate Professor Akira Takatsuki's Conjecture, Vol. 5 (light novel)

During the summer of his second year of university, to find out the truth behind his uncanny ability to detect lies and the Festival of the Dead, Naoya decides to head out towards the old village of Koyama in Nagano with Takatsuki and Sasakura. It was a village he visited many times as a child, the village where his beloved grandparents lived. But now, its no better than a ghost town. Reconnecting with his cousin, Naoya then hears of the ominous saying his late grandmother whispered until the day she died: Naoya was taken by the mountain gods. Arriving at the village where, according to the rumors the dead walk, the group begins their investigation. But suddenly, Naoya and Takatsuki are once again invited back to that midnight festival where it all began