At the end of the 19th century, the immortal detective Aya Rindo, now only a talking head after her body was stolen, is carried everywhere by her maid Shizuku Hasei. She takes on the half-oni oni-slayer Tsugaru Shinuchi, who has his own score to settle with whoever made him what he is, and the three travel across Europe, solving one supernatural case after another as leads toward Aya's body turn up. This manga adapts the original mystery novel and covers the same investigation the anime later dramatized.