Kêtai deka 3 the movie: Môningu musume. kyuushutsu daisakusen! - Pandora no hako no himitsu

Mei, Kai and Yui are high school students who also act as undercover agents and detectives dispatched to missions. The Tokyo police requests their assistance when a threat against the popular idol band Morning Musume has been received. They are dispatched to be with the band and guard them at their concert. All is well until one of the school girls disappears.