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"The Trick Diamond" is the key to unlocking a treasure hidden within Gaudí 's famous Park Gruell. The crime lord Mark Williams was in possession of the diamond but has recently passed away. However, his will gives Lupin a chance to gain the object of many a criminal's desire. Lupin is in for quite a shock though as Mark's conditions are quite unique. Mark replaced six treasures with copies and has kept the originals for himself. Now, Lupin must prove his talent by switching the originals back into place within seven days. Only then will he be given the location of the diamond.
Aired 01/08/2003EP 1 - Full

Lupin the 3rd: Operation Return the Treasure
Master criminal Lupin the 3rd is at it again! An elusive meteoric gemstone called the “Trick Diamond” was once hidden inside Spain’s Sagrada Familia cathedral. In pursuit of the diamond, Lupin receives a message from his recently-deceased rival thief, Mark Williams. Mark’s challenge: return the treasures!
Five treasures—all stolen by Mark in his heyday—must be returned to their original homes within seven days, or Lupin will never find the diamond’s hiding place. And Lupin is never one to waste a diamond! But scoring the Trick Diamond only gets trickier as Mark’s lovely assistant Fujiko is keeping more than one closely-guarded secret, and Mafia boss Ivan “Rats” Crockovich is trying to both obliterate the Lupin Gang and swipe the diamond for himself!
(Source: Discotek Media)