In the basement of the police station, there is a new department called "Special Investigations Countermeasures Unit". After disagreeing with her superior, Niizuma Tomoki is reassigned to this new unit under the management of Gonno Michinori. A single mathematician, Mikoshiba Gakuto, has been requested to join this unit as an observer. Gakuto is to objectively weigh the truth of cases through statistics and probability from observing interrogations by Tomoki. Can this method expose the depth of the human heart using only numbers?