At the car park of Interpol's regional office in Poitiers, inspectors Chase Devineaux and Julia Argent step off the elevator together. Chase is in the middle of a rant to his partner about his unsuccessful efforts to find and capture the phantom thief Carmen Sandiego. Julia suggests that they reexamine the penthouse that Carmen burgled but Chase is disinterested in pursuing that lead further. Chase bids Julia a good night but she reminds him that his gasoline may be low but is once again brushed off coarsely by the frustrated Chase. Unfortunately that is exactly the case and Chase steps out to acknowledge that Julia was right but as he does a woman and a man in black suits gas him and knock him cold. Julia returns to the car but is dumbfounded to find inspector Devineaux is gone and his car is not.
Meanwhile, in the waters of Ecuador, Carmen Sandiego is in the middle of a diving expedition, being guided by her loyal hacker and friend Player. Player and Carmen discuss the region's features as she explores the sea for a 19th century ship that sank in the area and could potentially catch the attention of the international crime syndicate V.I.L.E. Above the surface, Bostonian siblings Zack and Ivy are keeping a lookout from their fishing vessel; Zack lamenting his dislike of sea life while Ivy observes a nearby ship.
A short while later, Carmen manages to locate the wreck of the ship they were looking for. She heads below deck and finds a chest. After prying open the lock and rifling through the contents, she discovers an old doubloon within. Carmen sends footage of the coin back to Player but is interrupted before learning of its origin when the entire ship begins to shudder. From below the ship emerges El Topo, V.I.L.E.'s specialist in subterranean infiltration. Upon seeing Carmen has the doubloon, he knocks it from her hands and takes it for himself.
Above the surface, Zack and Ivy move their boat closer to the large ship. Ivy spots someone standing on the railing of the ship's bow, who immediately jumps directly onto their boat. It's Le Chevre, El Topo's partner and V.I.L.E.'s resident "from above" infiltrator. Under the water Carmen is busy chasing El Topo to get back the doubloon. As the two jockey for position to grab the coin, it's suddenly lapped up by a passing tuna. Now pursuing the tuna, Carmen almost catches up to it but the fish is ensnared by a net and dragged above the water. El Topo tries to pursue the boat that caught the fish but finds his face mask filling with water; Carmen had pulled his oxygen tube, forcing El Topo to surface. Carmen tags the boat with a tracker so she knows where to find it when it docks.
Meanwhile, Le Chevre is trying to interrogate Zack and Ivy, unconvinced of their story as local fishers. Hearing Player say the name "Carmen", Le Chevre infers it to mean "Carmen Sandiego" but before he can get any more information out of the pair, he hears El Topo calling for help. Distracted by his partner's situation, Zack and Ivy throw Le Chevre into the water and escape.
At the docks, Carmen inquires as to the whereabouts of the fish that she was chasing and is informed that it has already been sent to Ecuador's capital city Quito for auction. Player finally gets back to Carmen about the origins of the coin, confirming it was a doubloon but not of Spanish origin. Rather it was an Ecuadorian coin called an "Ecuador 8 escudos." This discussion catches the ear of a nearby woman, who inquires about Carmen's interest in the coin. She introduces herself as "Dr. Pilar Marquez," an archaeologist who was planning to study the shipwreck that Carmen had just come from. After convincing the doctor that they are coin hobbyists, Dr. Marquez explains the history of the coin and that it isn't a monetarily valuable trinket but does hold cultural significance due to being associated with Ecuador's independence. Though lacking in high monetary return, Carmen agrees to retrieve the coin for the doctor, rationalizing that V.I.L.E. isn't aware of this and would still steal it under the assumption it was a prized treasure, thus depriving Ecuador of a cultural relic.
Elsewhere, in a sealed room, Chase Devineaux slowly recovers from unconsciousness to discover he is handcuffed, being watched over by the two individuals who descended on him in the car park. The female agent pulls out a ballpoint pen and clicks it, dropping it on the floor where it stands on end. The top of the pen beams a bright blue light that projects the holographic image of a woman in a business suit with short hair. She simply introduces herself as "Chief" as the male agent deactivates the electronic handcuffs around Chase's wrists. She explains that Chase was brought before her in relation to the recent interactions he's had with Carmen Sandiego and hints that there may be a shared interest thanks to her work tracking a larger organization by the name of "V.I.L.E." Back at the Ecuadorian docks, Le Chevre and El Topo report in to Professor Maelstrom at V.I.L.E. headquarters. He instructs them to follow Carmen to secure the doubloon, for which he plans to melt down and turn into a pair of gold cufflinks that will make Countess Cleo envious.
Carmen, Ivy, and Zack drive up the mountainous roadway to the capital city of Ecuador, Quito. At over 9000 feet above sea level, Player warns the trio that they are in danger of succumbing to altitude sickness. Meanwhile, the Chief is explaining the research they have on V.I.L.E. to Chase. The Chief can only confirm six operatives of V.I.L.E. have ever been held in custody and none of them long enough to get any useful information out of, hence why she has struggled to pinpoint any firm details on the organization. Carmen Sandiego has been brought to her attention thanks to her various thefts of V.I.L.E.-affiliated targets, which is now why she wishes to bring Chase in on the investigation.
Arriving in Quito, the trio of white-hat thieves disembark only for Carmen to suddenly collapse upon setting foot outside the bus and pass out. She wakes up some time later in a tent. Delirious, she hallucinates that she's talking to Coach Brunt and mentions how grateful she was for being rescued as a baby in Argentina. However, in reality, she's being attended to by Dr. Marquez, who is helping her recover from altitude sickness.
Back at the Interpol car park, Julia Argent has been unsuccessfully trying to call Chase to ascertain where he went to if he didn't leave with his car. During this time, the Chief reveals that she works for an organization called "A.C.M.E.", the "Agency to Classify and Monitor Evildoers", which has now inducted Chase as a full-fledged investigator.
Carmen finally regains full consciousness and realizes where she is. Dr. Marquez confirms she had followed them to Quito, not fully believing their story of being a trio of rare coin enthusiasts. Carmen tries to leave on her own power but still hasn't completely overcome her altitude sickness, which causes her to become lightheaded and drop her bag. Her various gadgets spill out, confirming to Dr. Marquez that whatever reason she and her associates have to be in Ecuador, it is far more than simple coin hunting. In spite of her deception, Carmen convinces Dr. Marquez to let her help.
Ivy and Zack are checking all the fish at the auction house to locate the fish that swallowed the doubloon as Carmen arrives. Ivy proudly tells her she located the fish but lets it out of her sight and the fish is taken to the auction floor. Looking out into the auction floor, Carmen eyes Le Chevre sitting in the rafters. Knowing she can't deceive one of her former classmates, she tells Ivy and Zack to take the lead and acquire the fish as bidders. Zack, overzealously, takes this too seriously and bids "$150,000" for the fish, which everyone finds ridiculous. The lack of subtlety immediately catches the eye of Le Chevre, tipping Carmen's hand and allowing El Topo to move in on the target.
El Topo attempts to escape with the fish but Carmen trips him up. El Topo loses his grip on the fish but before Carmen can secure it, Le Chevre nets it out of her reach. Carmen attempts to convince Le Chevre that it's not the monetary value of the coin that he's stealing but Le Chevre is unfazed. Carmen grapples the fish and yanks both it and Le Chevre to the floor but, again, before she can move in on the fish El Topo snatches it up. As El Topo runs for the door, Ivy and Zack stand in his way. He takes a swing at them with the fish but only succeeds in slapping the recovering Le Chevre in the back of the head, which also dislodges the coin from the fish's stomach. El Topo helps Le Chevre out of the auction house, thinking they're escaping with the fish and the coin, but Carmen had already managed to take the coin for herself.
Julia is still trying to locate inspector Devineaux when she happens upon the mints he was chewing when he was first leaving the car park. Following the trail left by them, she notices they lead to a nearby door. The Chief is finishing her explanation of A.C.M.E.'s activities as a criminal monitoring network when Julia enters the room, revealing that Chase had only been dragged off to the side room for his briefing and not a far off location from the car park. Chase attempts to disavow any knowledge of Julia due to the highly secretive nature of A.C.M.E. but the Chief is surprisingly impressed by Julia's knack.
Carmen returns the doubloon to Dr. Marquez back in Ecuador. Dr. Marquez recalls her mentioning "Argentina" when she was still delirious, which inspires Carmen to possibly take a trip to Buenos Aires and figure out what significance it has to her past. Their conversation is cut short when Player informs Carmen that a string of art heists he had been keeping tabs on was likely to hit a major art museum in Amsterdam. Carmen boards the boat with her associates and they head off into the sunset.
- Evil Is Petty: Professor Maelstrom wants the doubloon, an object of little monetary value but significant cultural value, in order to melt it into a pair of cufflinks.
- Imagine Spot: While regaining consciousness, Carmen imagines that she is reunited with Coach Brunt, who turns out to be Dr. Marquez.
