Associate Professor Akira Takatsuki's Conjecture, Vol. 3 (light novel)

CURSES...BLESSINGS... TWO SIDES OF THE SAME COIN. A new string of mysteries begins with Naoya's classmate Nanba discovering a chain letter in his schoolbag. Unusually excited by the occult opportunity, Professor Takatsuki gleefully invites the burden of the chain letter onto himself! Meanwhile, an urban legend about a library spirit has been making the rounds. When Professor Takatsuki and Naoya take the case, they learn about a string of clues hidden within specific library books that will come together to reveal a secret message! But according to rumor, anyone who solves this cipher will fall victim to a curse...Later, the two make their way to the countryside to investigate the legend of a demon god worshipped in a rural village. But when an actual skull turns up in the cave said to house the demon's remains, it doesn't take long for the situation to spiral out of control...