David is cold. The best solution his advisors can come up with: lie with a naked virgin. Jerry Falwell, of course, would have you believe this was standard medical practice, old men fucking young girls. I'm sure it was very... theraputic. The unfortunately-named Abishag is brought to his bedside and does her best, but poor old David can't get it up even for her fine feminine attributes.
One of David's sons, Adonijah, sensing an opportunity, declares himself king. He recruits Joab the general and Abithar the priest to lend credence to his claim, but several other key players refuse to acknowledge him, even after he sacrifices some sheep. Personally, I'd be convinced by anything if there was barbecue involved.
But no, Nathan goes to Bathsheba, the woman David saw bathing naked from a rooftop and whose husband he had killed after he impregnated her. Nathan reminds Bathsheba that David supposedly promised to make their son Solomon his successor. How many soap operas has this plot appeared in?
So Bathsheba goes along to David's chamber, where Abishag is still uh, ministering to the king. She reminds him of his promise and asks him to depose Adonijah and put Solomon in his place. Nathan comes in and backs Bathsheba up. David agrees to make Solomon his successor. He orders his minions to take Solomon to Gihon on his mule and crown him. The people get so excited with their shouting and dancing that it causes an earthquake. Good thing they didn't have vuvuzelas, then.
Adonijah hears the trumpets and figures out the jig is up. He runs into the temple and grabs onto the altar, refusing to let go until Solomon promises not to kill him. Solomon promises that as long as Adonijah behaves, he can keep his head, and goes back to the party.