I don't have a precise plot in mind, but it would happen sometime after the end of season 1. Since I don't want to spoil it, the partner obviously has to have seen at least that far, and preferably through season 3 (as that's the end of where this could take place, for certain reasons). It would probably start with a violent confrontation and end with one subduing the other, followed by some angry hate sex. But that's just the most basic of templates; I'm open to suggestions! PM me concepts and such.
Err, edit: I'm playing Nina! I need a player for Jack.