Celestia and Luna meet one night, and have an entirely palindromic conversation.

(Inspired by a similar dialogue in Douglas Hofstadter's Gödel, Escher, Bach: An Eternal Golden Braid)

When ponies start appearing all across Equestria claiming to have traveled from the future, Twilight Sparkle and her friends must uncover what is going on. Why do the time-travelling ponies all die after only a few moments? How did they travel through time at all? Just what has happened to the future they are coming from?

Meanwhile there is growing turmoil in the Crystal Empire as there are increasing reports of attacks made by ponies formed of strange black crystal. As the ponies of Equestria grow more nervous about the events surrounding them, Twilight is faced with the most important question of all: Can the future even be changed?

Act I of Fragmentation of Harmony