Monster: Perfect Edition, Vol. 6 (Kanzenban #6) by Naoki Urasawa (Creator), Camellia Nieh (Translator)

Tenma learns from a resident that ten years ago, a woman with twins lived in an old apartment house in downtown Prague above a sign with three frogs. The neighbours also tell him about the Czech secret police and a suspicious fire.

Meanwhile, Suk reveals his investigation details to a beautiful woman named Anna without hesitation. Suk and Grimmer use the key for the safety deposit box to look for the contents related to 511 Kinderheim.
Then, two special investigators are killed in Suk's apartment and at the same time, Grimmer sees Anna leaving the building when he's on his way to see Suk. Tenma reads the news about Suk as a wanted person from the police force and former secret police. He knows the mastermind behind the killings and rushes to the hideout to save Suk, but when he reaches there, Suk is severely injured.

Colonel Karel Lanke, a high-level former Czech police wants to exchange Suk for the report and tape. Grimmer rejects the offer but allows him to listen to the tape. Tenma questions the Colonel about the fire and the kidnapping of a woman with twins by former Czech police. Colonel reveals that during those incidents, there was someone given authority to arrest people at his discretion, and his name is Franz Bonaparta. He is an author of strange children's books, and one of his books is called "The Nameless Monster".

Meanwhile, Inspector Lunge is taking his vacation in Prague. He discovers that the murder cases of the Czech ex-police relate to Anna when Suk's friends mention Suk's new trustable friend. Inspector Lunge goes to the Red Rose Mansion and finds a sealed door. Lunge brings the wall down and sees a painting of the twins' mother.