Six months ago, Lord Hugh Disward (Huey), lost his eccentric grandfather, Wes. To inherit Wes's estate, Huey must take guardianship over the 'Mystic Archives of Dantalian' that contains forbidden knowledge and a mysterious girl called Dalian. Dalian and Huey begin an unlikely partnership as they solve mysteries caused by Phantom Books.

Original Light Novel written by Gakuto Mikumo and illustrated by G-Yuusuke. Adataped to manga first by Chako Abeno, and again by Monaco Sena.