A teacher, who oversees Kindaichi's and Miyuki's report cards, accepts them both, though with one condition for Kindaichi, which is to catch the perpetrator of a prank, providing a photo image as a clue. Kindaichi accepts the condition, unaware that the prank would be a mere prelude for a serial murder case. Students were found successively dead by hanging themselves. What is the connection between this vengeful serial murder case and the suicide of Mitsuru Fukamachi a year ago and the mass suicide fifty years ago?