Ayumu Narumi, a contemplative freshman at high school, finds his life changed when he is blamed for a girl's fall from a school building. 
Using only keen observation and his stunning talent for deductive logic, he soons figures out the truth behind the incident and clears himself, to the amazement of his Police detective sister and Kiyono Yuizaki, the enterprising Journalism Club president. 
That case proves to be the start of a strange rash of crimes that Ayumu learns is the doing of the mysterious Blade Children. 
Over the objections of his sister, he investigates these crimes with the help of Kiyono who has considerable guile of her own. 
Meanwhile, the Blade Children learn of their new opponent and set about to stop him in form of deadly logic puzzles that will take all of Ayumu's brilliance to thwart. 
All the while, he uncovers dark secrets about himself, The Children and his connection to them.