An idea for a game I've been itching to play:
A lover is in love with his or her beloved, who is herself attracted to a third person, a victim. The lover, desperate for the undivided affections of his beloved, seduces him or her and gradually drives the beloved insane, turning her into a mad wretch heavily influenced by her lover.
The lover and the beloved, now both quite mad, kidnap the victim and kill the poor person, laughing as they do so. A few hours later, they realize what they have done, and coil into a self destructive spiral of love and hate, running from their own guilt, and from justice, to escape from a crime they may not even have actually committed.
I'm pretty flexible about the specific setting and character identities, and would be happy with any of the roles except the victim. I can also help brainstorm setting details for the story, which I intend to not be terribly long.