University student Yakumo Saitou, born with red eyes that allow him to see the dead, lives a life surrounded by spirits and unsolved mysteries. One day, a new instructor appears on campus—Gakuto Mikoshiba, a sharp-tongued yet absent-minded genius mathematician. This is the miraculous crossover of two beloved series by acclaimed novelist Manabu Kaminaga: the spiritual mystery "Psychic Detective Yakumo" and the logical crime-solving series "Probability Investigator". One solves cases through dialogue with the dead. The other deduces truth through statistical theory. Spirit vs. Science. Death vs. Logic. An unstoppable duo is born—ready to defy the very foundations of mystery fiction.