Fever Crumb is a prequel to the Hungry City books. Basically, this will set out how the world of municipal darwinism was built. You don't need to have read the entire Hungry City quartet (I had only read the first when I started the audiobook) nor will you be spoiled for that series by anything that happens here. There are some subtle connections in here, but they're mostly in the way of bonuses for fans of the previous series.The London here is rather different from the London of Mortal Engines, though you can see how it will end up there. The story mainly involves Fever herself, and her past, which is rather more interesting than she'd probably thought. It's also about a major upheavel in London, putting the city a step closer to municipal darwinism. It reads very much like the Hunger City books that I've read, with maybe a slightly lighter tone through most of it.
The audiobook is read by the author, and he did a good job of it. The audiobook also includes a bonus scene of baby Fever (a nice scene, but one that wouldn't have worked in the story as a whole) and a few minutes of Reeves talking about the inspirations for Fever and why he revisited the Hungry City world.