Luffy's brother, the infamous pirate Portgaz D. Ace, is being held at Impel Down prison...and he's scheduled for the chopping block! While breaking into the daunting underwater dungeon to rescue his next of kin, Luffy encounters former enemy Buggy the Clown and the toxically terrible Warden Magellan. Before long, what started as a prison break turns into all-out war with the World Government!