Ling Ling's estranged sister, Lang Lang, shows up at the Narutaki Detective agency unexpectedly. Six months prior, she had joined with Narutaki's rival, Le Bled, and ran away with him. Now, Le Bled has come for a showdown with Narutaki, and Lang Lang's visit is part of his plan. Lang Lang gasses Ling Ling and disguises herself as her sister, then tries to poison Narutaki. He, of course, is too smart for all that. When the plan is foiled, Le Bled appears, and tells Narutaki the only way to save Ling Ling is to defeat him in battle. The fight is joined, and Narutaki does save Ling Ling, but in doing so, Lang Lang and Le Bled are able to escape.