Goemon has been thrown into prison for a crime he did not commit. He is charged with cutting off the Little Mermaid’s arm. Roman, the Chief of the Copenhagen Tourist Bureau says he’ll release Goemon as soon as the arm is returned. Even though Lupin knows something is fishy, he signs on to retrieve the Little Mermaid’s arm from the Santa Maria wreckage with the help of Letizia, the dolphin. However, what the masterminds are truly after is the content hidden inside the Little Mermaid’s arm. How far will Lupin go to retrieve the arm and to avoid his pals getting arrested by Inspector Zenigata?