This one is a little different from my usual ideas, but I think it could be fun.
Three college seniors, a man and two women, live together in a small house off campus. They've been living together for roughly a year now, and while they might not hang out outside of the house, they trust each other and enjoy one another's company. One night, the three of them are watching tv, celebrating the fact that they all passed a big exam today, when an old black and white Superman show comes on. The show features Lois Lane tied up by the bad guys, and one of the girls makes some comment about how unrealistic it is that she can't escape. Everyone has had a little too much to drink, so the other girl makes a bet with her that she could escape before her friend if they were both tied up. The man agrees to judge the little contest and binds them both. It quickly becomes clear that all three of them enjoy the game, and the kidnapping club is born.
The rules are simple. As long as you don't have something major going on, either girl can be kidnapped at any time. Once you are kidnapped, you can be taken anywhere your kidnapper wants to take you, as long as it is safe. Basically I want to play out any bondage fantasies my partner and I have. (I think it would be easier if one person played both girls)Maybe one girl teams up with my character to kidnap the other, only to be double crossed at some point (or not), maybe my character grabs both of them and takes them to an abandoned little shack he knows about, ect.
Additionally, I think it would be fun if one of the girls had strong romantic feelings for the male character. Perhaps she even loves him, but he is utterly clueless about it. A real dom/sub relationship could start between the two of them that could even turn into a master/slave relationship.