When a number of female murder victims are discovered in Ueno Park with lilac flowers in their mouths and one of Shizuru's books by their side, rumor spreads that he may have some involvement in the case. Worried for her friend, Tsugumi learns that the murders seem to be inspired by a certain book where both Shizuru and Sasagoi-san have ties to the author. When Shizuru is taken away by the police for questioning, Tsugumi works with the rest of Fukurou to find the real killer before it's too late.
What's The Purgatory Island 
Murder Case about, anyway?
على أيّ حال؟ جريمة قتل جزيرة المطهر ما قصّة
Worum geht es in Mordfall
auf der Fegefeuer-Insel überhaupt?
¿De qué trata
Asesinatos en la isla del purgatorio?
¿De qué trata
Asesinatos en la isla del purgatorio?
Au fait, ça parle de quoi,
Meurtre sur l’île du purgatoire ?
Ma di cosa parla 
Omicidio sull'isola Purgatorio?
E sobre o que é esse Caso do
Homicídio da Ilha do Purgatório?
Причём здесь вообще
«Убийство на острове Ущелье»?