A woman named Michiko Oshitani from Shiga prefecture, was found dead strangled in an apartment in Tokyo. Matsuo Koshikawa, owner of the apartment also disappears without trace. Hiromi Asai's name appears on investigation due to her relations with Michiko Oshitani. However Hiromi Asai has a strong alibi and therefore the investigation cannot continue further. When detective Yuhei Matsumiya investigates, he finds a note at the crime scene. In the note, the names of 12 bridges surrounding Nihonbashi area are written. Detective Kyoichiro Kaga feels uneasy about this findings. This new clue reminds him of his mother who also disappeared suddenly.
