David's army is back in the thousands rather than the 600 he's been running around with for most of his story. His people beg him not to go and fight Absalom so he sends his generals instead, with orders not to kill Absalom.
The battle takes place in a forest, and 20 000 men die, approximately the same number of military deaths as on D-Day. The forest must share some properties with the island in The Life of Pi, because the wood devoured more people that day than the sword devoured (v. 8). Even Absalom is a victim. He's riding along on his mule when suddenly his head gets caught in a tree branch and he ends up hanging there, comically, by the neck.
Someone sees this, and when he picks himself up from laughing on the ground, he goes and tells Joab about it. Joab rebukes him for not smiting Absalom against David's orders, then goes and thrusts three either daggers, darts or javelins through Absalom's heart, depending which translation you're reading. Ten of his men witness this barbary and get in on the act, killing him again some more. Then they throw him very unceremoniously into a pit and cover his body with stones. This is somehow humiliating.
In a non-sequitur, we are told that Absalom had erected a pillar in honour of himself, because he had no son. Never mind that period of intensive reproduction when he was locked in his house and fathered no less than 4 kids in 2 years.
Then there's a weird dispute over who's going to tell David that his son is dead. Eventually they both leave. David sees them approaching from different directions. The first one doesn't have any news about Absalom, so David asks the second, who tells him his son is dead. This leads to David's famous lament: O my son Absalom, my son, my son Absalom! would God I had died for thee, O Absalom, my son, my son! (v. 33)
David is grieving dramatically, as is his style. Joab is disgusted and points out that the king loves his enemies more than his friends, because he doubts he'd be carrying on like this if his entire army had died and Absalom had lived. He tells him to get outside and give comfort to his people or they'll all abandon him. David goes, but this produces further confusion.
David calls for the priests and asks them to bring everyone together. They invite him back to Israel. Shimei, the stone-thrower from a couple of chapters ago, apologises to the king. Mephibosheth, Saul's son is next. David magnanimously gives him some land. An 80 year old man, Barzillai, escorts David and is invited to dinner. But Barzillai is a crotchety old man and only wants to go home. Why show up, then?
As David arrives, a dispute immediately arises between the tribe of Judah and the others over who owns more of the king.