In recent times, a mysterious private investigator under the name of "Spica" has been solving crimes before the police arrive, leaving only a star mark nearby to indicate her involvement. The true identity of this rising star is Lili Hoshizawa, an energetic 13-year-old girl who enjoys solving mysteries, athletic activities, and running her mother's fortune-telling business, "Fortune Teller Spica." Using her knowledge of astrology, Lili reads clients' horoscopes by day and catches criminals by night!

But Lili soon finds that her carefree, crime-solving adventures will need some more caution when her childhood friend Hiromi Oikawa returns from America and is suspicious of her and Spica. His extensive studies in criminal psychology seems to have helped him in solving mysteries—rivaling Lili's astrology and crime-solving skills. But this zodiac detective has no time to worry about a possible rival, for there are many cases and mysteries out there that she must solve in the name of the star!