Lupin and his gang break into a vault containing hundreds of diamonds. Unfortunately Zenigata shows up and a fire breaks out, and they have to leave with only a handful of their loot. Later, Lupin discovers every single diamond was a fake: a scheme involving counterfeit diamonds is afoot to raise the value of diamonds around the globe, and thus increase profits. Enraged at being conned, Lupin sets out to stop this scheme, but complicating the matter is Zenigata, who was informed that Lupin destroyed the diamonds. Lupin must now clear his name and stop the counterfeiters from making his job even harder than it needs to be.
—Tenchi