Somehow, somewhere away from Paris, Constance and Aramis end up on some sort of mission together in which they can't be known as who they are, and so are pretending to be husband and wife. I'd love all that could go along with this. Constance and Aramis bonding. Jealous d'Artagan. Constance and Aramis ending up in at least one sword fight together, or practicing swordplay, or Aramis helping her learn to fire larger weapons. All that.