When left to it's own devices Mollys hair can grow extremely long. Record making long, if she cared about such things.
During college and med school and all that she didn't have time for the upkeep and so kept it at a responsible length. But after she helped Sherlock fake his death she figures why not let it grow, all she has to do is go to sleep a little earlier so she can wake a little earlier to pin it back for work.
When (character of choice) finally sees her hair down for the first time it has an effect that no one could have anticipated.
Maybe Moriarty even decides to kidnap her, and keep her as his very own Repunzel.
Molly/Moriarty or Molly/Sherlock, Warnings: hair kink, possible kidnapping
During college and med school and all that she didn't have time for the upkeep and so kept it at a responsible length. But after she helped Sherlock fake his death she figures why not let it grow, all she has to do is go to sleep a little earlier so she can wake a little earlier to pin it back for work.
When (character of choice) finally sees her hair down for the first time it has an effect that no one could have anticipated.
Maybe Moriarty even decides to kidnap her, and keep her as his very own Repunzel.