I'm not going to rate this because it's just a novella and my opinions on it are more due to its form than anything else, so it wouldn't be fair.

Mysteries of Thorn Manor is a quick novella from the Sorcery of Thorns universe, and it really focuses on a short mystery/quest.
Thorn Manor has trapped its inhabitants inside, and with the Midwinter Ball approaching - which Nathaniel is supposed to host - they need to figure out why. One of the things I liked about the first book was that it didn't focus too much on romance, but the novella was more indulgent and that's part of the reason I'm not rating it...Elisabeth's inner monologue started to get on my nerves a bit. I've also said it before, but I'll say it again: I'm not a huge fan of cozy/low-stakes fantasy. That's another reason why I won't rate this novella because it was obviously not going to be very high-stakes from the beginning.
I did appreciate the Silas backstory, though. We still don't know much about him (especially thanks to the epilogue), but we do get a few hints throughout the story, and he's still my absolute favorite character from this series.
I really hope the author continues the series soon because I am desperate for answers about Silas.