A man enters Scrooge's office to claim a 200 year old debt. The man introduces himself as Chisel McSue and gives Scrooge a paper.
The paper tells how 200 years ago, Swindle McSue put captain "Seafoam" McDuck in charge of delivering a horseradish cargo to Jamaica. Seafoam signed the contract without reading the fine print, sice he didn't have his glasses. Seafoam's ship sunk during the travel and he only managed to save his gold teeth. When he returned to his mansion, Seafoam found Swindle McSue there, explaining that the fine print said that if the horseradish cargo didn't reach Jamaica, Seafoam should give all his belongings to Swindle. These included Seafoam's gold teeth, but he refused to give them and ran away.
Scrooge then reads the current contract, saying that since Seafoam didn't give the teeth away, Scrooge must give all his belongings to McSue. However, Scrooge has his glasses on, and reads the fine print saying that McSue cannot take possession until 30 days, and never will if Scrooge manages to complete the original contract.
Scrooge goes to Donald, Huey, Dewey and Louie for help. He explains that one way to complete the contract is to give his ancestor's gold teeth, but he sold them years ago to invest the money. The other way to complete the contract is to find the horseradish cargo and deliver it in Jamaica. Donald tries to dissuade him, since the cargo sank 200 years ago and they don't even know where.
Scrooge prepares a ship anyways, but before sailing out, Huey, Dewey and Louie manage Scrooge to sign a contract ensuring that he will pay for their help. From time to time, the ship stops so a frogman can explore underwater to find Seafoam's ship; Scrooge does it the first time, but Donald takes the frogman duty from then on. Donald finds a place where there are no fish, but Scrooge dpesn't care, and later chastises Donald for getting treasure from other ships instead of seeking for horseradish.
The search takes several days. One day, Scrooge is going to eat his lunch, but when he finds out that the salad is horseradish, he throws it away as it reminds him of his unsucessful search. Donald sees the horseradish falling to the sea, and notices that every fish stays away from it, so he suggests to return to the place they found the first day where there were no fish. When they return, Donald finds Seafoam's ship and its horseradish cargo, and also discovers that Swindle McSue sabotaged the ship 200 years ago.
Meanwhile, Chisel McSue talks with a friend about his upcoming fortune, when they hear the radio news telling that Scrooge sent a message offering a reward to anyone who can take him to Jamaica to bring horseradish. McSue and his friend take a motor boat and reach Scrooge ship, shooting and sinking it. Then McSue tries to kill his own friend as he is an eyewitness of his crime, so when McSue falls from the boat, his friend leaves him.
The Ducks, who survived the sinking, carry the horseradish box on a raft. They find McSue drowning and Donald tries to save him with the help of the kids. Donald asks Scrooge to help them saving McSue, and while Scrooge refuses at first, then he notices he cannot let him die and all five ducks save the villain. The ungrateful McSue kicks the horseradish box overboard and then tries to kill the Ducks, but Donald decides it has been enough and all them defeat and tie McSue.
Scrooge is depressed as he will lose his fortune, while McSue is still happy, as he will soon become the richest man in the world. A ship finds the raft, saving the six castaways, and the nephews tell the captain that Uncle Scrooge will pay him for bringing them to Jamaica, as they knew McSue would kick the horseradish box, so they secured it with fishing lines.
At Jamaica, after leaving the cargo, Huey, Dewey and Louie tell Scrooge to pay them for their help. Scrooge tries to not pay, but the kids tell him the fine print states that if he doesn't pay, he will have to eat every horseradish from the box. Scrooge pays the kids while Donald laughs at the fact.