Scrooge McDuck buys a boat to be used on Friday, not knowing he's being spied by a man pretending to be blind. The "blind" man goes to report this to John D. Rockerduck and Jeeves, who decide to follow Scrooge by putting a device on his boat. Meanwhile, Donald goes to see Gyro Gearloose, who shows him a giratory boxing punch to train, but Donald doesn't want it.
At Friday, Scrooge invites Donald, Huey, Dewey and Louie to a cruise, so they can push the boat to the sea, but Donald gets the idea to set sails and use the wind to reach the sea. Scrooge reveals the boat motor works with pedals, but Donald and the kids don't work until Scrooge promises them a part of what he's seeking, the treasure of Edward Teach, otherwise known as Blackbeard. Rockerduck, Jeeves and the fake blind are following the ducks from a submarine and see when Donald dons his diving suit. Donald dives and finds Blackbeard's ship the Revenge, but it was booby-trapped by Blackbeard centuries ago, so it explodes, but the first explosion produces a chain reaction that throws the treasure chest to the surface.
However, the only thing inside the chest ia a single doubloon, and made of iron for worse. Scrooge decides that he should exhibit it at his museum, but then Rockerduck swipes it to have it in his own museum. Jeeves and the fake blind break the Ducks' boat and then leave alongside Rockerduck in the submarine. Dewey uses his Junior Woodchucks training to lasso the submarine periscope and be remolcated.
Inside the submarine, the fake blind notices strange drawings carved on the doubloon, but Rockerduck only cares for it because Scrooge wanted it. When the fake blind sees by the periscope that they are remolcating the ducks, Rockerduck orders Jeeves to submerge, so Huey must cut the lasso. Donald finds Rockerduck's device used to find them and they must pedal back to Duckburg.
At Donald's House, the kids read in the Junior Woodchucks Guidebook that the iron doubloon wasn't the treasure, but actually the map to Blackbeard's treasure. The kids try to formulate a plan to recover the map, but are too tired and go to sleep. Donald also pretends to go to sleep to change ito the Duck Avenger.
The Duck Avenger goes to Gyro's house to get the giratory boxing punch and then goes to the beach to find the hiding place of Rockerduck's submarine, inside a cave under Rockerduck's house. The Avenger puts Rockerduck's spy device on the submarine and then calls Rockerduck from a phone booth, pretending to be Scrooge. He tells Rockerduck that he has found Blackbeard's treasure, so Rockerduck decides to follow him with the submarine again, not knowing his device will make them follow themselves.
The Duck Avenger enters Rockerduck's house by the window and awaits. When Jeeves finds the device on the submarine, Rockerduck returns home. When Jeeves sees the broken window, the fake blind deduces Scrooge may have stolen the doubloon, but Rockerduck tells he has had it in his pocket the whole time. Then he finds a chest and opens it, but it's the giratory boxing punch the Duck Avenger left there, and it knocks the villains out. The Duck Avenger takes the doubloon and leaves.
The following morning, Scrooge arrives to Donald's house to tell he has read in a book about the map, and Donald reveals he has it as "his friend" the Duck Avenger gave it to him. The ducks travel to the island of the map (which is casually owned by Scrooge), where Donald tries to sleep on a hammock, but he falls and accidentally falls on the treasure. Scrooge and the kids return with him after finding nothing, and Scrooge tells Donald he will give him the island, and Donald makes the kids promise to build a cabin if they want to vacation in his island. Then he reveals the treasure he found, telling the Duck Avenger told him where to seek it. While Donald rests and Scrooge enjoys his treasure, Huey, Dewey and Louie must build the cabin and besides get water, firewood and fish.