I want to be with Tamar, but I can't because she's my sister.
I have an idea. Pretend to be sick. Your father will come visit you, and when he does. . .
Yes. Can you send for my sister Tamar to come and make me food? Maybe if I see food prepared in front of me, I would want to eat.
Do you need anything my son?
David had a beautiful daughter named Tamar. The daughter of David and Ma'achah, and the sister of Avshalom.
Lay with me.
Never! It's against the rules of Bnei Yisrael! You're my brother! Ask our father, and if he says yes, then I will.
Her half-brother Amnon was lovesick for her (Mostly because she's a virgin). But he knew that he couldn't be with her because the Torah prevents it. So he goes to his friend Yonadav for advice.
I hate Amnon! I going to kill him for what hed did to my sister.
Come Tamar, let us go to my house. It's okay he's only your brother.
Amnon pretends to be sick so that his father wuld come and visit her. And asks him something:
Okay. I guess.
Tamar comes and prepares food for Amnon just like her father commanded her, but Amnon still doesn't want to eat it. He recommends "maybe if I'm in bed I would want to eat it." and sends out all the servants from his home while Tamar follows him to his room.
Amnon, knowing what their father would say, rapes her. But soon after, he gets sick of her and forces her to leave instantly, and locks the door behind her. when she leaves, she starts mourning, and her (full) brother, Avshalom sees her and invites her into his house to stop people from staring.
Avshalom prepares for a sheep shearing party and invites a lot of guests. He goes to his father and asks if any of his siblings could come. Amnon in specific.