I acquired a significant amount of forest green velvet some months before season 8 premiered, and new as soon as I saw this episode what I needed to use the velvet for. Unfortunately, it was almost an entire year before I was able to construct this costume.
The bodice pattern was designed by me, and was the result of many muslins cut and sewn until I was satisfied with the shape.
Close-ups of the costume being worn in the episode reveal that the front closure is a zipper, and I figured if the BBC wardrobe could cheat, so could I.
The brooch was two separate pieces glued together so that I could fit a blinking blue light behind the cameo (the light came from a children's ring).
The wig was styled from a lace-front I already had, and took a little over a few hours to curl and style.
The front contrast on the bodice and skirt is an old curtain.