Neverwhere is a supernatural/fantasy novel by Neil Gaiman, first published in 1996. The protagonist, Richard Mayhem, lives a normal life in London with his beautiful fiancee and with his boring office job. His life turns upside down when he stumbles upon a bleeding young woman in the middle of the city and decides to help her despite his fiancee's threat to cancel their engagement. Richard later finds out that the woman he's helping is being hunted by people that want her dead. Richard's decision to keep helping her pulls himself down from the safety of the London he knows to the dangerous yet alluring realm of London Below.
Now, I want to talk about things that I don't like first. It's the main protagonist. I feel like his presence is weak compared to other characters and the writer's effort to make him shine more in the story feels really awkward and confusing. I think that's the writer's intended outcome, but it's hard for me to figure out the tails or heads of what am I supposed to feel of him. There's also one giant plot hole that kinda ruins a badass moment of a character. Plot holes are generally acceptable as long as you can work around the logic a little bit, but I gave up trying to figure out the logic behind this moment's plot hole.
Besides those huge problems that I mentioned above, everything else is great. The London Below caught my attention the most by its depiction of a whole new world under the warm lights of London, spinning a lot of the city's landmarks with new interesting mythologies and backgrounds. The supporting characters, Door, de Carabas, Hunter are all awesome. They add more flavors to the story, whether through their own personal struggle, personality, or meaningful decisions throughout the story.
Overall, if you're really into Gaiman's storytelling, I think this one would be a huge treat for you. If you aren't, however, I'm afraid you would be quite disappointed.