I now know why there's no mystery-romance sub-genre. Romantic suspense is as far as it gets because it's damn hard to have a real mystery with a romance. I think it's time to tweak the plot here. Romance is still the name of the story (A Cold Winter's Night), and there's definitely a mystery, but I'm thinking suspense rather than bringing them together at the end.
Or maybe tweaking the romance? Hmm, there might be an idea. Change that up a little, make it work in the mystery setting. That might be the way to go here.