Immortality. Many have vied for it. None have obtained it. But Lupin the Third has yet to try!

A gemstone named the Mermaid's Scale appears in a secret, underground auction, and Lupin is coerced by the queen of the underworld into stealing the rock for her. Lupin however quickly discovers not only that the stone is a forgery, but that the real Mermaid's Scale is part of an unsolved riddle involving the mysterious girl Misa that leads to transcending mortality.