Kaito Daimon is a typical high school student, except for one remarkable trait: he is a "demon" when it comes to solving puzzles. His brilliance is such that when he is asked to take some "special" tests of his unique ability, he immediately suspects that the test itself is a riddle. Kaito suddenly finds himself swept into a deadly Philosopher's Puzzle created by the sinister group POG—a lethal maze of trap after trap, where failing to solve the secret correctly means death. Fortunately, Kaito's skills prove up to the first challenge, both for himself and for his childhood friend Nanoha, who is also caught in the deadly scheme. But now that he has been designated as a Solver, he is pulled into a new existence where he must travel the world alongside other Solvers, attempting to solve the latest deadly enigmas left by POG. There is a new conundrum around every corner, and each deception could lead to death, but once a riddle is presented, Kaito can be counted on to unfold, unravel, and unlock it.