Absalom: had a beautiful sister.
Amnon: also had a beautiful sister, that he lustfully desired.
Tamar: was the sister of these two brothers
David: the father of these two brothers
Jonadab: Amnon's friend.
Amnon shared his lustful desires with his friend, Jonadab. Instead of rebuking Amnon, Jonadab encouraged the wickedness, and helped him devise a plan to carry out this deed.
Thus, Amnon raped his sister, Tamar.
King David heard of the plan, but did not intervene. Even after his own daughter was raped, King David did not act on her behalf.
Absalom's anger eventually led to him killing his brother Amnon for raping his sister, however: "the anger of man doesn't produce the righteousness of God"
So many men failed Tamar. So many family members failed Tamar.
What could each of those men done differently to protect Tamar?
Be men. Act with love.