Excerpts from the Journal of Twilight Sparkle, recovered by Canterlot Interdimensional Expeditionary Force on Sojourn #4, approximately 2 Equestrian Years after last contact.
After the whole "Horror in Canterlot Incident" Trixie had been sent to an insane asylum until she was deemed sane. Unfortunately for her, the previous dealing with the Herald and his old Tome might not be over yet.
Pinkie Pie is worried that Twilight is getting too caught up in her work. She has to convince her friend that the Great Old ones aren't all that scary. Stop thinking about them, Twilight.
In the years since Luna returned from the moon, she’s always been quiet about the truth of her exile. Always keeping it to herself, hidden away. Keeping secrets. She never even told Celestia that something was up there with her.
In the blink of an eye, all life was wiped from the face of Equus by an abomination born of the stars. That is, all except for four immortal Princesses. Now they fight for the only thing they have left other than their grief... revenge.