Ai, who works in the Special Fraud Unit of the Investigation First Division, has been attempting to make contact with a 'groundworker' group that has been causing trouble on the streets recently. After working for a month at a snack bar used by the group for negotiations, she finally manages to catch their tail. She is then proposed to impersonate the proprietress of an old-established inn called 'Yukawa-ya,' and begins an undercover investigation... It's a 100 billion yen case, an absolutely unforgivable failure, but in the final stage of uncovering the whole truth, the developer who appears before Ai as a buyer is her husband of all people.
