A man has been arrested for killing a girl, but when he isn't indicted, he returns to mock the girl's family. As Chief Inspector Kusanagi of Tokyo's Homicide Division knows, however, the same man was accused of a similar crime two decades ago, but got away scot-free. During a parade, the suspected killer dies unexpectedly, but the people with all the best motives have rock solid alibis. In this fourth case (after A Midsummer's Equation), Kusanagi turns once again to his college friend, physics professor Manabu Yukawa—known as Detective Galileo—to help solve the string of impossible-to-prove murders.