Ageha Shiraishi has been sentenced to death as she was suspected of murdering her four roommates. In her prison cell as she awaits her execution to be processed, she tells her gatekeeper, Kyousuke, that she is innocent and that she did not commit murder. Kyousuke does some research, but finds that she is still guilty. Upon his return, he finds his superior tied up and stripped. After setting him free, he finds out that he has been tricked, and it was Ageha in disguise.

He is surprised to find Ageha can impersonate anyone to the finest detail, whether it be hair color, habits, or even voice. Ageha thus becomes the first fugitive of the Talsis Prison and she declares that she will find the real culprit. Kyousuke now only has one clue: "the Ageha" tattoo (swallowtail butterfly) on Ageha’s back.

The chase between Kyousuke, Ageha, and the real culprit begin as they move to grasp the truth!