"Pearl of Wisdom" is the twenty-fifth episode of DuckTales.
Down in the tropics lies a small piece of land known as Banana Island. Heading towards the island is a submarine operated by Pete, who goes by the name Sharkey for this episode, and his assistant Yardarm, a skinny, anthropomorphic dog. Sharkey and Yardarm are traveling to Banana Island in hope of there being something of value that is worth stealing. While spying on the islanders through the sub's periscope, Sharkey discovers a large pearl in the hand of a stone idol, which he intends to steal, and goes through his disguises. Yardarm says it sounds like a plan worthy of a master criminal, or a plan worthy of blissing to a little diabolical laughter, and starts to laugh. He and Sharkey then laugh maniacally.
That night, Sharkey, who has disguised himself as a fellow islander, goes after the pearl, while bringing along Yardarm, who is hiding in a fruit basket. While Sharkey distracts the islanders by dancing for them, Yardarm snatches the pearl with an extendable, mechanical claw. The two crooks leave the island, and Sharkey already knows who he can sell the pearl to.
The next day at McDuck Manor, Scrooge is on the phone with his shipping company, and complains about how he has a whole fleet of cargo ships which are not in use for anything. Huey, Dewey, and Louie tell Scrooge and Webby about a marble-shooting contest going on in Duckburg Park later in the day, and how they want to enter Huey. Webby herself is also interested in shooting marbles, and runs off with the boys.
Sharkey shows up at the door, posing as the not-so-French entrepreneur Monsewer Ratt, and has Duckworth escort him to Scrooge's study. Meanwhile, the boys struggle to find their marbles, to which Webby tells the boys to clean their room to achieve their goal. With no other choice, the boys get to work in order to find their marbles, including a shooter referred to as the Great Masher. Meanwhile, Monsewer Ratt has sold the pearl to Scrooge for $100,000 and leaves, but Scrooge is happy because the pearl was worth more than he paid for it.
When Sharkey returns to his convertible, Yardarm, who did some reading while Sharkey was gone, tells him that the pearl may very well be the legendary Magical Pearl of Wisdom, which can grant infinite wisdom. Scrooge, who was informed that the pearl came from Banana Island, puts the pearl away in a display case and heads off to the Duckburg Explorers Club to learn more about the island, hoping that possibly more pearls could be found there, or bananas, as far as Duckworth is concerned.
Webby, who does not have a Great Masher of her own, asks Scrooge if he has one she can borrow while he leaves the house. Not really paying attention to what Webby just said, Scrooge agrees. In a hurry to get to the park in time for the contest, Webby spots the pearl and takes it, thinking that it is actually a Great Masher, replacing it with one of her own marbles. Sharkey and Yardarm spot Webby as she leaves the house with the pearl, and follow her.
At the Duckburg Explorers Club, Lord Battmountain informs Scrooge that if he really does have the Pearl of Wisdom, returns to the island and stands in the surf at dawn while holding the pearl, he will be granted infinite wisdom for a short period of time. Scrooge likes the idea, as he could use the wisdom to expand his financial empire, but Lord Battmountain reminds him that it is probably just a myth.
Sharkey and Yardarm follow Webby in their car as she rides to the park on her tricycle. Since too many people are around, they do not have an opportunity to steal the pearl from Webby. Eventually, they follow Webby into the park on foot, while Officer Burley writes them a ticket for parking next to a fire hydrant. Meanwhile, Duckworth discovers that the pearl has been replaced with a marble, which reminds Scrooge of the marble contest. After freaking out, Scrooge heads over to the park to retake the pearl.
At the park, Yardarm attempts to grab the pearl back from Webby, but ends up ripping a hole in Officer Burley's pants, causing Burley to write Yardarm and Sharkey more tickets for breaking various laws. Scrooge shows up just as Webby is about to shoot the pearl, and she messes up her shot, causing the pearl to bounce away. While Scrooge, the boys, and Webby go after the pearl, a squirrel runs off with it, but tosses it away when it realizes that it is not edible. The chase ends near a lake, where Yardarm manages to snatch the pearl and flee away with Sharkey in their car, while Duckworth drives after them with Scrooge and the kids. Sharkey and Yardarm reach the docks, where they take off in their sub.
Scrooge goes after the crooks in one of his cargo ships, as it has sonar that can detect the sub. The ship manages to catch up with the sub, but not without Sharkey and Yardarm finding out. The crooks respond to this with a torpedo aimed at the ship. Luckily, Huey manages to set the torpedo off prior to it hitting the ship, by shooting it with his Great Masher. Afterwards, the boys give a mourning speech of the sacrifice of the Great Masher. Thinking the missile has hit, Sharkey and Yardarm leave and manage to reach Banana Island first, and arrive early in the morning before dawn. This time, they are holding the islanders captive by threatening to shoot them with the sub's cannon. Sharkey is excited because he will soon have enough wisdom to pull crimes of the century every day.
Scrooge and the boys, who are dressed in stealth gear, head to shore in a raft. As Sharkey gets ready to stand in the surf, Scrooge and the boys sneak over to where Sharkey is, disguising themselves as bushes. They manage to sneak right up to Sharkey, which is when Scrooge grabs the pearl right out of his hand. Yardarm shoots and almost hits Scrooge, and although he does not hurt him, the pearl does go flying out of his hand. Two of the nephews fire marbles where Yardarm is standing, causing him to lose his balance and blow a hole in the sub, sinking it.
Scrooge and Sharkey fight over the pearl, and by the time the sun rises, they both wind up holding the pearl at the same time. As a result, they are both granted with temporary infinite wisdom. Sharkey then concludes that he will end up in jail if he continues to steal. Scrooge realizes that the pearl truly belongs to the islanders, and that he should not use it for mere profit. The leader of the islanders explains that the pearl's magic allows one to make the right decisions, in addition to the proper and most fulfilling ones. Thus, Scrooge returns the pearl to him.
In the end, Scrooge, the kids, and the crooks all wind up partying with the islanders. The leader explains that even though this was not the first time the pearl was stolen, it had always found its way back to the island. Scrooge then concludes that the islanders have far too many more bananas than they can possibly eat, and agrees to sell the surplus bananas for them, which he can transport around the world with his cargo ships. As such, both of them would profit.