Enter Sabo! The Boy From the Grey Terminal

Luffy discovers that at the end of the forest is a slum dumpster named Gray Terminal, a lawless area full of homeless people. While Luffy searches for Ace, Ace attacks two men carrying treasure and robs them. Luffy then sees Ace running towards the forest to meet Sabo and follows after him. He ends up discovering their secret stash, much to the two older boys' panic. Luffy gets captured by the crew who’s loot Ace stole when Luffy is asked where the money and valuables are, he tries to lie unconvincingly. Soon Sabo figures out that Luffy won't ever tell Porchemy. And so he and Ace run to Luffy's rescue.