I've never read Ms. Derr before, but I will look for a longer piece. This story was quite simple, not fleshed out and had some jarring moments. Even fairy tales, which this seems to be, should be factual, if items and situations that truly exist, are mentioned.
Though no specific place is mentioned, we do have a time period, set by the mention of beheadings as a form of death. I'm not sure what tar and feather murders are, as tarring and feathering was used as a form of punishment and I found no mention of it used as a death sentence, but then I did cursory research.
Though there were mentions of cigarettes, matches, pocket watches, cravats (1610,) these were all things that existed in times when beheadings were practiced.
I was jarred when the king referred to the prince as Your Highness,as I don't believe the king would give such deference. After all, he is the king, THE Royal Highness, if you will. There was a reference to the prince as My Lord, which is incorrect. He would be Your Royal Highness.
The idiom, champing at the bit, was first found in Rev. Charles Lucas's religious poem, Joseph, in 1810.
Casual violence was minorly disturbing and there were times when I couldn't imagine the hero accomplishing the deeds he did, particularly since he was injured throughout. The build up to the prince finding out that Diggory was his affianced was delicious, but then fell flat, almost an afterthought.
I don't rate on length of pieces, as that is the length the author chose to write. However, within the bounds of the presented word count, this could have been a truly wonderful story with more depth to the characters, the period, and the spell put on Diggory. I wish the ball scene had been longer and more seductive, but again, I don't rate on what I wish it was. The arrest of Benoit was anticlimactic and non-confrontational. We never got to see Diggory as a prince, in full command.
I love the premise of the two princes being betrothed, without any explanation or eye batting. We should live in such a world where two men can marry without hand wringing. That premise kept me reading.