After the conclusion to Borderlands: The Pre-Sequel, Handsome Jack learns that Tassiter hid a powerful, top secret code deep within Claptrap, dubbed the H-Source. To extract the H-Source from Claptrap, Handsome Jack digitizes his Vault Hunters and sends them inside Claptrap's mind to obtain it. What seemed like a simple task turns out to be not so simple... (borderlands.fandom.com)