With Abner dead as a doornail, it's Ishbaal's turn to go on the chopping block.
When he gets the news of Abner's death, he's dismayed and disheartened, as are all the other people in the northern kingdom of Israel.
Also, Ishbaal has two captains of raiding teams—Baanah and Rechab, who are Benjaminites.
Then, in an apparent digression, the narrators say that Jonathan (Saul's son and David's friend, now dead), had a son named Mephibosheth. He became lame after his nurse dropped him as a baby, when she was fleeing after the deaths of Saul and Jonathan at the hands of the Philistines.
Natural Born Killers
At any rate, these two raiding captains, Baanah and Rechab, decide to kill Ishbaal. They go into his house at noon, acting like they're going to ask for wheat, and then they chop his head off and take it with them.
They ride all night and bring Ishbaal's head to David at Hebron, proclaiming their loyalty to him.
However, this doesn't make David happy. He says that he killed the Amalekite who helped Saul commit suicide, so why won't he kill them too, for killing the son of the Lord's (formerly) anointed while he was taking a nice siesta at midday?
So, David has his men kill Rechab and Baanah—they cut off their hands and feet, and then hang their bodies near the pool at Hebron (thus disrupting some water volleyball games, most likely).
But they bury Ishbaal's head respectfully, putting it in Abner's tomb.