II Samuel - Chapter 13
A Rape and a Murder
David had a son named Avshalom (Absalom). He had a sister named Tamar. Another brother, Amnon, lusted after Tamar.
The exact relationship between Amnon and Tamar is not made clear. They were probably half-siblings, either children of David from different mothers, or perhaps Tamar had the same mother, but a different father. In either event, they appear to be half-siblings or step-siblings, but not full siblings. (Tamar and Avshalom were full siblings.)
So, as we said, Amnon lusted after Tamar. His friend Yonadav gave him the following advice: Amnon should pretend to be ill and request that his sister Tamar be sent to care for him. (It is not stated whether Yonadav's intention was that Amnon abuse Tamar, as he ended up doing, or whether this was just a ruse to get some "alone time" that Amnon took too far.)
So Amnon did as Yonadav suggested. When Tamar came to his room, Amnon sent his servants out. Then he raped her. She begged him not to, saying that if he spoke to David, he would surely permit them to marry. (If they were step-siblings, she may have meant it. If they were half-siblings, it was probably just a stalling tactic.) When he got what he was after, the sight of her sickened him and he cast her out in her torn, disheveled clothes, locking the door behind her.
Tamar's brother Avshalom found her crying and figured out what had happened. He comforted her and resolved to take care of Amnon but good. David found out and was angry about it, but he did not punish Amnon publicly, possibly to avoid a scandal. Two years passed...
Fast forward: Avshalom was making a feast to celebrate the shearing of his sheep in the territory of Ephraim. He invited his father King David to attend. David declined. So Avshalom said, "Well, at least send Amnon to represent you!" David thought this request was a little strange, but he agreed to it. Avshalom then instructed his servants that, when he gives the signal, they should pounce on Amnon and kill him. This they did.
When the king's other sons saw Amnon attacked, they feared Avshalom was murdering them in order to make a coup. (Remember how Avimelech killed his brothers, the sons of Gideon, in Judges chapter 9?) They mounted their mules and fled. A rumor reached David in Jerusalem that Avshalom had, in fact, killed them all. Yonadav was there and he figured out what must have happened; he assured David that only Amnon must be dead. (Charming fellow that he was, when David's other sons arrived, he basically said, "See? I told you so!" Keep in mind that none of this ever would have happened if not for Yonadav's bad advice in the first place, so he's the last one who should be gloating!)
Avshalom knew he'd better not go home, so he ran away to Geshur. (Talmai, king of Geshur, was his mother's father - see chapter 3, verse 3.) Avshalom stayed in Geshur for three years. David mourned for Amnon and longed for his estranged son Avshalom.
The Mishna in Pirkei Avos uses the story of Amnon and Tamar as a model of what true love ISN'T. A dvar Torah by this author on this topic can be found on the NCSY web site here.