After pulling a heist at a Moscow Casino, Lupin and Jigen went to visit Mark Williams. An old thief that Lupin knew well. Only to find that Mark has past away recently. Lupin and Jigen then went to Mark's estate to find the Trick Diamond. Which wasn't there. That Diamond is a key to opening the secret treasure of Gaudí's famous "Park Gruell".However they were met by Fujiko who showed them a prerecord message from Mark when he was still alive. Mark tells Lupin that if he could replace 6 of the items with the copies, Mark had stolen then he'll find the Trick Diamond. But Lupin has 7 days to accomplish this request.So Lupin accepts the request and receives a digital camera from Fujiko so he could take a picture of each item in it's original place.The adventure begins as Lupin travels throughout Europe to return the treasures to their rightful places. But there is a man named Rats who wants that Diamond for himself. So he hires some hit men to hunt down Lupin's gang and try to kill them. But it'll take more than that to stop Lupin from doing a favor for a deceasist friend.Operation: Return the Treasure is a pretty good Lupin the 3rd TV special. The animation is very similar to "Episode 0: The First Contact". And the story is unique with action, humor, realistic scenery, and never a dull moment.It's another yet to be in English Lupin title. You're able to see it only in fan subs at the moment.