Princess Luna, a mare without friend and a princess shunned by her subjects often finds herself often on nigthly strolls around her home, trying to figure out how to help her both her sister and Equestria.

The story takes place roughly a pony lifetime before the ascent of Nightmare Moon and was inspired by 'Children of the Night'.

Read the follow-up here: http://www.fimfiction.net/story/50554/How-Sisters-Collide