It was an interesting challenge writing this story. It had to:
• Be a complete narrative on its own while fitting into the overall arc of the trilogy.
• Reveal something interesting about the characters but nothing so important that readers would need it to understand the main books.
• Be fun to read!
At its worst, a secondary story (or DLC in a story based game) can feel empty and pointless, where you meet a bunch of watered down secondary characters and follow stories that are so removed from the main plot as to seem irrelevant.
The trick seems to be to deepen the experience for the reader, allowing them to enjoy the other books in a richer way, without damaging the main stories for those who haven’t read the shorter works.
I feel like the comics do this sort of thing on a near daily basis, with Neil Gaiman’s Sandman series being a standout example, where a number of smaller human stories (each complete narratives) feed into the greater mythos of Dream and the Endless. Often, Dream is a pivotal but secondary character in these stories.
Another example that comes to mind is the Mass Effect series. There are three games (that function like a trilogy), and each has DLC that provides extra content and adventures. One of my favourite bits of DLC was the Lair of the Shadow Broker mission. Not only did it include some dramatic locales, but there were was a reveal about one of the secondary characters that changed my relationship with the third game.
I also feel like I’d be a bad human not to mention The Split Worlds short stories by *cough* Emma Newman. There are over 50 shorts that focus mostly on the minor characters so that when they appear in the main books, the readers get a sudden rush in recognising who that delivery boy is, or knowing the real reason why a particular uncle is always so grumpy. Again, you can read the main books without them, but for readers who like to go deeper, they’re a perfect addition.
So what about The Vagrant and the City? Well…
The Vagrant and the City is set about five years after The Malice. Most of the major characters appear in it, with the story showing how they are responding to the changes at the end of book 2. It also sets up things for The Seven. We follow the Vagrant as he is set to work by the Empire of the Winged Eye, and gain further insight into the people of the Shining City, and some of the interplay between them and the colonies. Goats may also make an appearance at some point.
I’ll leave it up to you to judge whether it works or not.