Kaitou Saint Tail is about a girl named Haneoka Meimi who is in middle school. During the day, she is a typical teenager, but at night, she transforms into Kaitou Saint Tail! Mimori Seira is Meimi's bestfrind, and the only one who knows of Meimi's secret identity. Seira is a nun in training. People who have had something stolen from them, come and pray at the church. Seira then tells Meimi about it and later, at night, St*Tail gets the stolen item back. She only steals to help people.
Asuka Jr's father is a detective who is trying to figure out who St*Tail is. Asuka Jr joins the chase. Meimi has fun leaving clues about where and when she is going to strike next for Asuka Jr, who is her crush.