The Pentagonal Future
The plot is after an ecological disaster -- think A Canticle for Leibowitz, here. My female MC ends up in her worst case nightmare situation, and an age inappropriate male MC moves in to attempt to salvage the situation. And So IT GOES OFF... The deterioration of life as we know it, the growth of a new society, a very strange new society, shaped to insure the survival and sensible continuation of traditions that create sustainable life to replace that which has been ruined.
(Some of this is written somewhere)