The Straw Hat Pirates arrive at Gran Tesoro, a ship and entertainment city ruled by Gild Tesoro. The concierge Baccarat gives the Straw Hats a VIP stay due to their fame, and they go to a casino, where they win a lot of money. Baccarat then takes them to the VIP lounge to meet Tesoro, who challenges them to a dice game. However, Baccarat uses her Devil Fruit abilities to strip Luffy of his luck, causing him to lose. She reveals her foul play and the Straw Hats refuse to give up their money, causing them to fight Baccarat, Tesoro, and his subordinates Mr. Tanaka and Dice. They are overwhelmed, and Tesoro, who can manipulate gold, captures Zoro by manipulating the gold dust sprayed on him when he entered Gran Tesoro. Tesoro gives the Straw Hats until midnight the next day to repay their debt, or he will execute Zoro.
Outside, the Straw Hats run into Carina, a former acquaintance of Nami’s who is now working for Tesoro. They hatch a plan with Carina to steal money kept in the main hotel, and find out that most people in the city are enslaved to Tesoro. Tesoro pays CP-0 agent Spandam to send World Government forces after the Straw Hats. The next day, the Straw Hats split up into two teams and infiltrate the hotel. Team A, Luffy and Franky, scale it from the outside in order to disable its surveillance network. They disable it, but are caught by security. Tesoro and Tanaka then confront them, and Tesoro binds Luffy’s arms in gold before Tanaka sends them plummeting into the Golden Prison, a large cavern filled with nothing but gold.
Luffy and Franky meet Raise Max, a legendary gambler and member of the Revolutionary Army who takes them through a dangerous pipe system to get to a seawater pipeline and wash the gold off Luffy. They reach the pipeline after Max stops a giant spinning fan. Meanwhile, the rest of the Straw Hats and Carina sneak into the room containing the money, only to find themselves on a stage as part of a trap laid by Tesoro and Carina. Tesoro reveals that he knows where Luffy and Franky are and attempts to drown them by flooding their location with seawater. He then attempts to execute Zoro, but when trying to release liquid gold from Gran Tesoro’s fountains, seawater comes out instead. Carina’s group reveals that they had intended for all of this to happen in order for the seawater to be released, and the seawater frees everyone from Tesoro’s control by washing the gold dust off them. Luffy and Franky’s group emerges from a fountain, and the Straw Hats reunite as Gran Tesoro’s citizens and prisoners rise up against Tesoro and his crew.
Intent on remaining in control, Tesoro blows up the hotel and forms it into golden armor for his subordinates and a giant golem that he occupies. The Straw Hats fight Tesoro’s crew, and Luffy goes after Tesoro, but is overwhelmed. Marine forces led by Rob Lucci then attack Gran Tesoro, and Spandam captures Luffy. However, Sabo intercepts Lucci, and a child that Luffy inspired saves him from Spandam. The Straw Hats defeat Baccarat, Tanaka, and Dice, and Luffy uses Gear Four to destroy Tesoro’s golem. Tesoro turns the golem into liquid gold, which traps everyone except Luffy. Tesoro attacks Luffy with a massive tendril of gold, but Luffy destroys it and defeats him, sending him flying into the Marine fleet where he is arrested. Everyone is freed from the gold, but Gran Tesoro then appears to go into a self-destruct protocol. Carina decides to stay behind while everyone else evacuates, and as the Straw Hats depart, they realize the protocol was false and Carina now has control over Gran Tesoro. As the Straw Hats are chased by the Marine fleet, Carina sails Gran Tesoro into the distance.