I know that one! There are actually two very similar stories, one is part of the 5th Season and its called Faster than A Speeding Bullet by Sheila Harper and I can't find the other one right now, but they are very similar. There is an nfic and a gfic for both I believe.

Come on Lois you havent said a word since 1866!

Thanks for the avatar, Hana.