This is a contemporary urban fantasy. There is a sentient 'alternate Swansea', co-existing with the present-day one but stuck in a 1940s timewarp. It is possible for some people to travel between the two Swanseas, and the alternate one has a small population of misfits. While in the alternate world, they do not need to eat or drink, fall ill, grow old, or die of natural causes.
The plot concerns a threat to the alternate Swansea by a being called the Ragchild. There are various plot threads, following characters in both Swanseas whose lives gradually converge as the final contest draws near.
For once, a short book which I finished in a couple of sessions. Not a book for children; it's quite brutal in places and the language is strong. The 'sense of strange' of the alternate Swansea was quite well done, and the main characters well drawn. I liked it because it was so different - as a result I suspect it will stay in my mind for a long time, and I will keep it for a future re-read.