“The job of a ‘detective’ is to carry out a case to the very end!”

An enigmatic box of chocolates arrives at Butt Detective’s office.
Inside the box, there’s a hidden message from his former partner, Suisen, with whom he worked 10 years ago...
It’s a request to solve a major incident that occurred at the Metropolitan Museum of Art, where she works!

However, Butt Detective is confused by how much she has changed compared to the past...
To uncover the biggest mystery in the history of the series, Butt Detective sets his plan into motion!