Pretty Boy Detective Club: The Pretty Boy in the Attic novel volume 3 was written by NISIOISIN.

Mayumi Dojima is finally a full-fledged member of the Pretty Boy Detective Club, known to her compatriots as Mayumi the Seer, she of the beautiful eyes. Summoned suddenly to the disused art room that serves as the club’s headquarters, Mayumi is pressed into service to assist with an ambitious redecorating project. But when they discover a secret room containing thirty-three mysterious canvases, the Pretty Boys are faced with their most perplexing puzzle yet. Who is responsible for these strange paintings, and are they connected to an impossible kidnapping that took place at Yubiwa Academy seven years ago? The third installment of the Pretty Boy series offers a beautiful mystery with an even more beautiful solution!