A phantom thief named Rusty Nail sends a letter to a mansion, saying they're going to steal their treasure. The Mikuni Detective Agency is called to protect the treasure, but are they up to this challenge?
The team randomly runs into Rusty Nail at a supermarket. Rusty declares that she will get back at them for ruining her last job by stealing something from their agency. Will Takumi and the others be able to protect their agency?