The Furthest Station

The blurb for this novella covers the basics: Peter investigates ghosts on the Underground and they lead him to an investigation of a more corporeal crime at the furthest reaches of the Metropolitan Line. The result is the usual mix of police procedural and magical fantasy, with an irreverent tone offset by the more serious nature of what may have happened once that's revealed in the second half.

It clearly fits into its slot in the series, but doesn't rely too much on previous continuity. The short length means that Abigail isn't front-and-centre very much, but she's clearly going to be playing a bigger role in later stories, and the grounds for that are being laid here. There's also a new character introduced who we'll doubtless see more of, even if he's a bit young to be doing much at this point. As a novella, it keeps zipping along, a short break between the full-length novels and perhaps with less of the darker side than some of those.

There are also brief in-character notes for the benefit of American readers; I can't speak for how much they'll really be needed but it's a nice touch.