My rating: 4 of 5 stars
A short novella. Story wise, it does exactly what it says on the tin. Minor spoilers in the review below. You do need to have read Neverwhere before reading this follow on, as it happens concurrent to the events in that book.
The Marquis, during the plot of Neverwhere, is relieved of his precious coat. Croup and Vandemar essentially kill our Marquis, and dispose of his body. Luckily, the Marquis had a back up plan, and he can therefore continue in his quest and get his coat back! And also, eventually return to his responsibilities in the main story of Neverwhere.
A very enjoyable reminder of the world of London Below, the sewer people, the rat people, and all of the other varied inhabitants of that other world.