Chapter 526 is titled "Adventure in the Great Prison".
Hancock (with Luffy hidden under her robes) and Vice-Admiral Momonga arrive at Impel Down and are greeted by the Vice Chief of the prison, Hannyabal. Hannyabal apologizes for being ambitious (saying "my Impel Down"), and says that Chief Warden Magellan is on Level 4 and that they will be guided there by Hannyabal and Domino. Domino says that since they do not have much time, they will have to quickly conduct a full-body check. As they proceed, Domino explains that when prisoners arrive, they are disinfected, sterilized, and then "baptized" in boiling water before being imprisoned. She continues by stating that some of their recent arrivals, Crocodile, Jinbe, and Ace, did not even bat an eyebrow during the process, which is very impressive.
Domino then leads Hancock to a private room to check her, and asks her to remove her mantle for inspection. She offers Hancock some Seastone handcuffs, but Hancock quickly turns her and the visual Den Den Mushi to stone with her Devil Fruit powers. Luffy emerges from beneath her robes, and Hancock says that she is sorry that she was not able to take Luffy further into Impel Down.
Luffy thanks her for getting him into the prison, but Hancock asks him not to cause a ruckus, as he will be unable to escape if caught. Luffy promises her to do so, and then hides in the ceiling until Domino is finished and leaves the room with Hancock. Outside, Hannyabal reports that the visuals to the room are back, and Domino apologizes for taking too long with the inspection. Hancock is disgusted to be handcuffed, but Hannyabal says that these are rules, and that there is nothing to be ashamed of.
Hannyabal points her toward the lift to the lower levels, and Luffy successfully escapes the room and continues. On the lift, Hannyabal says that they can proceed straight to Level 4, but that it will be hot. He tells Hancock to be prepared, and says that while they are moving, she should enjoy the screams of the prisoners on Levels 1 through 3. Hancock sees Luffy and prays for his fortune, but mistakes his thank you as "I love you" and faints, much to the confusion of the jailers. Luffy turns away and pulls out his Vivre Card to find out where Ace is. Seeing the card pointing downward, Luffy heads out into the prison.
In another part of Impel Down, the Blue Gorillas have just returned from retrieving meat from Sea Kings. In the monitor room, a jailer reports that they have found Buggy, who was last seen on Level 1. Buggy, who heard the broadcast, punches a visual Den Den Mushi and runs, much to the amusement of the other prisoners. Some Blugori run past trying to catch Buggy.
At the same time, Luffy, following the Vivre Card, comes to a large door. He manages to sneak past the door when some jailers open it to catch Buggy. Luffy arrives at Level 1: Crimson Hell, and is asked by some prisoners if he is escaping. Luffy says he is from the outside, and asks where Ace is being kept. The prisoners tell him that Ace is most likely being kept on Level 5, where criminals with bounties over 100,000,000 are kept, and ask him to get the keys for them to escape.
Luffy then notices someone running from the Blugori, and sees the man get sliced in half. Luffy turns and runs, and notices that the man is Buggy, who is stunned to see Luffy in prison. Buggy wonders if Luffy was caught, but Luffy says that he entered on his own accord. Buggy thinks that Luffy came to save him, but immediately doubts that. Luffy tells him that he was trying to not cause trouble, but they notice more Blugori ahead and Buggy says that they will be tortured if caught. The two then turn and attack their pursuers, changing their plan to an uproar.
- Vice Chief Hannyabal is introduced.
- Luffy is able to sneak deep into Impel Down.
- Ace is apparently being held on Level 5.
- Luffy "reunites" with Buggy on Level 1.