Mona Lisa Smiles Twice

The famous painting, "Mona Lisa," is going on a rare international exhibition. Zenigata shouts far and wide that Lupin will come for it. But Lupin has personal reasons in this case. The truth is that his ancestor once was stuck with a fake. The security system in the floor of the exhibition hall is tricky: unless one walks the correct pattern, it will promptly become a pit. There are any number of Mona Lisas. What of the "true" Mona Lisa?