The letter is used in the Royal Trouble quest. After the player returns the Heavy box full of stolen Etceterian goods, which Queen Sigrid falsely accused King Vargas of stealing, she writes this letter as a formal apology and asks the player to deliver it to Vargas. Players who attempt to read it will be given a choice of whether to proceed or not, since the letter is not addressed to them, however there is no consequence for reading it. It reads:
Vargas, I'm sorry to tell you I won't be declaring war. Your Regent has uncovered a plot to make us distrust each other, and I'd rather have my own reasons to go to war than be tricked into it.
Your Regent told me about the snake (s)he killed (you made a good choice of (her/him) as ruler), and how our kingdoms are linked by caves. Perhaps we should be working on our dungeons together.
And if you ever find someone to take that yeti curse off you, please let me know. You're a warmongering fool, but so am I. I think we'd be well suited to each other.