During the course of his travels to find Blackbeard, Ace befriended the milk maiden Moda after she saved his life, and in return, he infiltrated the naval base G-2 to deliver a message to Vice AdmiralComil. During his undercover stint, he inadvertently helped reunite Moda with her parents, and acquired information on Blackbeard.
On an island somewhere in the Grand Line, Ace runs away from a restaurant after eating without paying, with the chef he ran from giving chase. When he reaches the dock, he stops to ask people for information on Blackbeard. However, his searching only leads him to find a man known as Dr. Black Beard. Not realizing that he has the wrong person, Ace kicks Dr. Black Beard, which causes the angry villagers to literally kick him into the river. Being a Devil Fruit user, Ace nearly drowns in the river, but after going downstream, Ace is rescued by a girl named Moda. She then takes the unconscious pirate to her house on her family's dairy farm, where he eventually wakes up. Ace and Moda officially meet, and Moda asks him to deliver a letter for her. In exchange for saving his life, Ace agrees to deliver a letter.
Ace goes to the G-2 Marine base, where the letter is supposed to be delivered. He swiftly defeats a Marine soldier and takes his uniform as disguise to infiltrate the base. He then finds himself in the dining hall, where he helps himself to some food. However, he overhears a Marine badmouthing Whitebeard and clobbers him, blowing his own cover. He was able to escape the Marines chasing him by beating up a Marine commander and taking his clothes as well while also eating his meal. In a different part of the Marine base, a meeting quickly turns sour because the coffee is extremely bitter. Even the commanding officer, Vice Admiral Comil, hates it.
Elsewhere, a marine scout ship approaches the base, but it gets set on fire by some pirates. The Marines are very worried because top-secret documents are on the scout ship, when one of them jumps into the conflagration. The Marine turns out to be Ace, who carries some documents as well as an unconscious Marine out while still on fire. However, this causes the Marines to quickly deduce Ace's identity and chase him down again, but he was able to evade their attacks thanks to his Logia powers. Before escaping, Ace hands Moda's letter to Comil, the intended recipient, while still being shot at. Comil reads Moda's letter, which asks the Marines if they would like to buy her milk.
A Marine food ship stops by Moda's home to purchase her milk, and it is revealed that the cooks on the ship are Moda's parents, who happily embrace their daughter. Due to now having her milk, the Marines' coffee tastes much better. Meanwhile, Ace sails off, having gotten information on Blackbeard from the Marine scout ship, and is now ready to find and take on the traitorous pirate.