Remi, a bunny-eared girl who runs a tiny detective agency with her little sister, receives an anonymous letter enclosing a generous advance and an invitation to stay two nights at a secluded mansion. Eager to cover living expenses for the two of them, she sets off for her client’s residence.

Waiting for her at the mansion are four animal-eared trainee angels. Sent to the human world before graduation to learn how mortals think, they must pass Heaven’s “Graduation Reasoning Project” by reasoning like a human before they can become full-fledged angels.

Yet the assignment proves far trickier than Remi expected, and this bizarre case refuses to crack in a single night. Meanwhile, one of the angels seems to be catching on to her other identity…