Mars has been terraformed and, slowly, is being colonized. Conditions there are still hostile, with low temperatures and a terrain still resembling the Grand Canyon on Earth. The air, however, is breathable, and the planet rich in natural resources which corporations and governments on Earth are eager to take advantage of. While mining communities are being set up and civilization spreading, it's nothing like the cities of Earth in size or in order.
The characters - both female - are two central figures in one such mining community, a small town of just a few hundred people, if that. One is a doctor, providing medical services mainly to the miners, but also the local militia tasked by the governments and corporations of Earth with keeping the order. The other character is a member of this militia, a marine from Earth.
At the onset of the story, the two are in the beginnings of a relationship. It wouldn't be appropriate to say they're madly in love or anything like that, but they are not strangers, and have a mutual interest in each other.
Conflict arises between the two when, demanding increased productivity, Earth tightens its hold on the miners, pushing them to work harder. The workers fight back, by going on strike and demonstrating. This, in turn, leads to even tighter control, and things begin to spiral out of control. The two characters, the doctor and the marine, are caught more or less on separate sides, which of course puts their sympathies, their duties and their feelings for each other at odds. From that point on, the story can develop naturally in any direction – or it may diverge in some separate direction at an even earlier point.
If this sounds interesting, do let me know!