After successfully robbing the Monte Carlo Casino, Lupin The Third and Jigen Daisuke soon learn that their money is in fact counterfeit and they go after the man

responsible: Count Lazare de Cagliostro.

The two soon find out that the Count is behind something far worse than counterfeiting money for casinos: he has been keeping a family secret hidden deep in his castle.

Can Lupin find out what this is and live to tell the tale? With the help of Jigen and the wise samurai Goemon Ishikawa XIII, Lupin is hell-bent on finding out the Cagliostro family's secret fortune and make it his own.