This episode is devoted to the classic scene of the Mahabharata in which Krishna reveals to Karna his true descent. He never was the Son of a Suta, which everyone called him with scorn. No, he was in fact the eldest of the Pandavas-- the original Partha. Now that the truth was out, all Karna needed to do was embrace his Dharma, join his brothers, and assume the title of King of India.
Poor Karna, always the victim of bad timing. It was way too late for such an offer. Perhaps if Kunti had stood up and claimed him as her son during the Pandavas' first military exhibition, he might have come around then, but now there was too much water under the bridge. Karna had been tossed out as a baby like the day's garbage, and had been scorned as a Suta when he tried to display his Kshatriya nature. His modest Suta parents and the evil Kauravas had been the only ones to come to his aid, and he would never give them up.
Krishna failed in turning Karna, but somehow he allowed Sanjay to know of the entire conversation, so the story of Karna's descent and temptation was made known to all the Kauravas. Kunti caught wind of the encounter, and she made a go at turning him. She also failed, but she at least got the promise that he would spare her other sons, and should Arjun die, Karna would take his place as her fifth son.