One Piece Episode 422 titled “Kesshi no Sennyū! Kaitei Kangoku Inperu Daun” means “A Deadly Infiltration! The Underwater Prison Impel Down!” is aired on October 18, 2009.
In this episode, Garp tell to Ace that Luffy already knows about his parentage and that he had hoped Ace and Luffy would become marines. And Ace answer that it is impossible because both he and Luffy are descendants of the best criminals. The Buggy Pirates sail towards Impel Down,they are hoping to free the captured Buggy. Hancock reaches Impel Down with Luffy, where she meets with Hannyabal, the ambitious vice-warden of the prison, and is to be subjected to a strip search before being granted entry.
Source: Mega Video