This game was ranked highly on the 'best exceptional story' poll on the fallen london reddit recently, and I wanted to check it out.
Turns out that it gives out huge chunks of backstory and lore regarding the royal family. This one story helped clear up the plots of Ambition:Nemesis, Sunless Sea, and Sunless Skies more than any other single story I've read on there.
You are given a strange doll, and it eventually leads you into the depths of the Shuttered Palace. There you encounter the royal family as they now are, after the transformations of the fall.
It's not as long as some of the other fate stories (most of CMG's are longer), but it has a hefty chunk of content, especially if you slow down and read everything. In terms of impact of the lore revealed, it is very high overall.
The writing on this piece was well-done, exactly the kind of thing you want in Fallen London (where you're left wanting more, but then more is offered...at a cost).