Batman: The Killing Joke

While out on patrol, Batgirl (Barbara Gordon) fails to stop a robbery, but manages to stop one criminal with help from Batman. Paris Franz, the robbers' leader and the nephew of a powerful mob boss, develops a dangerous obsession with her and starts sending her messages. After Franz tricks her into finding his uncle's dead body, Batman becomes concerned about her safety and takes her off the case, telling her that she will eventually be tempted to kill the criminals she pursues. Outraged, Batgirl attacks Batman physically and verbally, which leads to the both of them having sex. A few nights later, Batgirl tries to apologize to Batman, but he is ambushed by Franz and his men, prompting her to come to his aid. When she arrives and overpowers Franz, he makes her lose control and give him a savage beating, stopping just short of killing him. Realizing Batman was right, she retires from crime-fighting.