A mysterious killer calling himself the "Quartering Duke" has recently begun a chain of murders that have claimed over 100 lives. As chaos spreads throughout society, the government announces unusual countermeasures against the Duke.

They're enlisting the help of the Detective Alliance, an organization comprised of the very best in their field. Referred to by others using detective aliases, these individuals are regarded for their heroism as the crime rate continues to rise year after year.

Ordinary high school student Wato Hojo is one such admirer of the Alliance. One day, he crosses paths with a peculiar man calling himself "Senior Detective," who informs Wato that he's been selected as a member of the Detective Alliance. Following this, Wato is knocked unconscious and forcibly brought to a remote island whose very name is unknown to him.