A fork in the road, or a branch shooting off of a river. It's a fairly common metaphor for what happens in a temporal decision point - the place where a choice splits the stream of time off into new directions. But time flows ever onward - once past a point of decision, going back and taking the other route is no longer possible. Even seeing down that path is relegated to the realms of the imagination. Or, at least, so it seems.
Princess Luna has finally learned from her sister of one of the secret treasures of Canterlot, a treasure obtained during the time Luna was absent from Equestria. A treasure neither gold, nor gems, but pure knowledge - the factual knowledge, at least in part, of what happened down those other streams of time. Please, join with Luna as she investigates the stories within the Book of Other Days.
Celestia seems out of character at first, but then the reasons for her strong reaction to Luna becomes apparent later. Archaic Luna is archaic, though she used a 'dost' when it should have been a 'doth.'
All in all, a great story so far. I'm especially intrigued by the notion of all those books, and what they might contain.