A princess team-up story? I'm going to love this.

So..., Twilight couldn't remember getting any weird letters, and Luna couldn't detect any trace of a spell. Did I miss the evidence that made them focus on mail-bomb spells?

If the vision had been imbedded in a letter then it is quite unforuntate that the Equestria mail system does not use tracking numbers.

Between pony Twi and Sunset, they should be capable of finding out at least something. Next chapter time.

I smiled. “Twilight, you have a poor grasp of villainy,” I said, earning a nod from Luna. “If she vowed vengeance on Starlight, then she wouldn’t change targets unless it would affect her as well. We tend to be single-minded that way.”

I love the self awareness here!