Kimi to Boku no Kowareta Sekai (Our Broken World) was the first Nisioisin book I didn't like. An attempt to write a traditional mystery novel, this resulted in page after page of the detective character tediously explaining every exhausting detail of the deductive process for a mystery that wasn't interesting to begin with. Sure, the detective might be a high school girl that refuses to go to class and spends all her time in the nurse's office, selling her own body, and the narrator had an icky subplot about his incestuous relationship with his sister, but neither of those elements could make up for the dire tedium at the novel's core.
After writing it, someone once asked Nisioisin for a sequel, and he made up this title as a joke, and then eventually actually wrote the thing. I have a tendency to keep buying everything authors I like put out, even works of theirs I don't really care for, but he put out two more novels in this series before I actually got around to trying the second one.
It's at times like these that my compulsive buying justifies itself, because this was one hell of a book. This time around the detective character (cousin of the original) does not endlessly explain things...at least, not directly. She actually never says a word. Somehow she is able to communicate vast swathes of information through facial expressions alone. She also fails to survive the book, a fact the illustrations helpfully reveal dozens of pages before she actually gets murdered. Structurally, this book really manages to subvert the problems he ran into in the first book; after a chapter spent introducing the characters, the narrator's sister winds up dead, and he and the silent detective begin investigating. In drag. She always wears the boy's uniform, and he decides to solve this thing wearing his sister's spare uniform. After a comparatively painless if labored explanation of the trick used in the murder, they fail to actually narrow it down to a final suspect, and he is forced to go try to rattle a few things loose and see what happens. This is where all hell breaks lose. Not only does the detective die, but the killer herself gets murdered by one of the other suspects; it all sort of leaves a bad taste in your mouth, the way murder really ought to I suppose, not least because the characters are mostly thirteen. But come to think of it, Nisioisin's mystery works have always been really good at making the actual murders viscerally unpleasant to read about. It's all part of his more manipulative side; by rattling the reader's emotions he sets us up to buy it when the other shoe drops.
In this case, the other shoe drops in the epilogue, when the detective from the first novel rings the narrator's doorbell, and neatly flips the entire book on his head. Nisioisin's done the unreliable narrator trick before, to great effect, but I'm pretty sure he topped himself here. Easily the best actual mystery novel he's written...even though the mystery itself is nothing you can't work out for yourself, he had enough cards up his sleeve that he was able to turn the tables on me at the very end.