This is a big day in the war. Bhisma fulfills one of his oaths by killing Dushasan and drinking his blood. Now he will be gunning for Duryodhana.
Arjun & Karna finally get busy with their final showdown. The whole universe apparently took sides in this conflict, with everyone choosing a champion to cheer for. The pair begin fighting with conventional weapons, but soon escalate to magical weapons.
At one point, Arjun gets the upper hand, and strikes Karna until he's lost his wits and drops his weapons. Arjun then allows his opponent to recover somewhat before they resume fighting. Krishna scolds Arjun (not for the first time!), for failing to strike the enemy when he's down. Arjun has quit arguing with Krishna over these things, so he resolves to kill Karna at the next possible opportunity.
At this point, Fate and Mother Earth have had enough and they intervene directly. Mother Earth seizes Karna's chariot wheel, bringing her enemy to a halt. Karna jumps down to pull free the wheel, but it won't budge. He asks Arjun to think of the Warrior Code, or his Dharma, and not to fire until he could fix his chariot and get moving again.
This annoys Krishna, who scolds Karna for even bringing up the subject of Dharma. Where was his Dharma when Draupadi was molested? This speech both shames Karna and enrages Arjun, who finally obeys Krishna's orders and kills his enemy.
There's that wheel again! What does it mean that in the course of this war, we've had a Wheel Formation (that killed Abhimanyu), and Arjun's son dies using a Chariot wheel as his only weapon, and then Karna dies, clinging to a wheel which was stuck in the earth. Is there some deeper meaning to the image of a wheel in this war?