At a posh birthday bash for a prominent politician, Zenigata's probe into a forged Lupin calling card is disrupted when Lupin himself arrives unexpectedly. Amid the pandemonium created by a group of masked attackers, Zenigata chases Lupin and finally corners him in the estate's courtyard. Shortly thereafter, Zenigata is wounded by a shot fired from a window that Lupin identifies as originating from his own gun, prompting the master thief to launch his own investigation. As it turns out, the assassins who stormed the soiree hail from a secretive isle known as the Island of Assassins. Protected by officials from around the world who manipulate its lethal inhabitants for their own benefit, the island is rocked by a convoluted conspiracy that fractures its population. Lupin, alongside cohorts Goemon, Jigen, and Fujiko, find themselves embroiled in the turmoil, while also gaining insights into Lupin's past and his previous endeavors prior to partnering with Jigen.