The Detective Is Already Dead Novel Volume 10 is written by Nigozyu with illustrations by Umibouzu.

Kimihiko Kimizuka, working as the Ace Detective's assistant to recover the lost records of the world, comes to the conclusion that Arsene, the Phantom Thief, may be the cause of this strange phenomenon. Believing the identity of the Phantom Thief to be the world's worst criminal, Abel A. Schoenberg, they seek out the Assassin, Fuubi Kase, who once chased Abel. What they finally discover is the tale of a battle between justice and an enormous evil—the truth of the Akashic records hidden away by the world!