Yuzuru Hamura is a university student and a fan of mystery novels. Against his will, he was forced to join the school's mystery club. The club is led by Kyosuke Akechi. Meanwhile, Hiruko Kenzaki appears in front of them. She attends the same university and she is also a private detective. These 3 people attend a summer camp and stay at Shijinso pension in the mountains. On their first day there, they must barricade themselves in the pension. The next morning, they discover a murder has taken place in the pension.