Reiko is a rich heiress to an industrial and financial business conglomerate, but she chose to work as a detective. She resents her superior, Kazamatsuri, who always seem to be making illogical deductions that causes murder cases to become cold cases. One day, her butler suddenly announces his retirement, and he chooses Kageyama as his replacement. Reiko realizes that Kageyama's deduction skills are very good after Kageyama solved a seemingly unsolvable mystery. Now, set on the Princess Reiko, the largest luxury liner in Asia, the sharp-tongued butler and Detective Reiko are challenged to solve a puzzle against 300 other passengers and crewmen.