This is something that has fascinated me for a while, but no ones been free or interested in playing this out with me, so, here goes.
I could be a Marine working in a covert base, working on crossing to alternate worlds. The one I go to is different, as the Axis powers won WW2. I could be trapped there and are taken in by the resistance, where I tell them the truth, and try to get their help to repair my controller, which is the only way to get me back to my own world.
Alternatively, I could be from such a world, and my partner could play a soldier or something from the world that we all know, who finds his way there. I'm thinking it would be set in Seattle, or San francisco, perhaps San Diego. As we know its a major US naval base, which a victorious german navy would also want.
Either one works for me, whichever one you like best.