Neverwhere is a fantasy novel that follows the hapless protagonist Richard as he finds himself accidentally drawn into the magical world of London Below-a place that is literally right below the city of London, but contains things beyond Richard's wildest dreams. As he teams up with the Lady Door, the Marquis de Carabis, and a mysterious woman called Hunter, Richard discovers that there are important things than a quiet life. This novel explores themes of identity, heroism, and reality.
Neverwhere is the story of Richard Mayhew and his trials and tribulations in London. At the start of the story, he is a young businessman, recently moved from Scotland and with a normal life ahead. This breaks, however, when he stops to help a mysterious young girl who appears before him, bleeding and weakened, as he walks with his fiancée to dinner to meet her influential boss.
The morning after Richard rescued the girl, named Door, from the streets, she is greatly recovered, and sends him to find the Marquis de Carabas, a man who will be able to help Door escape two infamous and seemingly inhuman assassins, the Messrs Croup and Vandemar. Richard brings the Marquis back to his apartment to meet Door, only to see both of them vanish immediately. Soon after, Richard begins to realise the consequences of his actions. He appears to have become invisible; he loses his job, where no one seems to recognise him, and his apartment is rented out to other people.
Determined to set things right, Richard tries to enter the world of London Below in search of Door. He finds a tramp from Below, who is the only person able to see him, and recites the name of the Floating Market as the only place known to him in underworld. The tramp brings Richard to the realm of the Rat-Speakers, who worship and perform tasks for rats. They attempt to assault and rob Richard, but follow orders from the master rat and let him free. He then travels across the mysterious Night's Bridge, whose darkness kills Richard's Rat-Speaker friend and guide, Anaesthesia. Eventually he arrives to the Floating Market, where he meets again with Door, who is holding an audition for bodyguards. Going to the Market, a giant bazaar where people barter for all manner of junk and magical items, Richard realises that London Below is not such a bad place.
The legendary bodyguard and fighter "Hunter" joins their party, and the group, consisting of Door, the Marquis and Hunter, with Richard tagging along, sets out for the Earl's Court. Door and the Marquis have previously travelled to Door's home and discovered a diary entry made by Door's father, which advises her to seek aid from the angel Islington. When the four reach the Earl's Court, on a mysterious underground train which follows its own bizarre schedule, the Marquis is forced to leave. This is due to an old grudge between himself and the Earl. The rest discover that they need to travel through the relic Angelus to reach Islington, and that the Angelus resides in the British Museum.
Door and Richard travel to the Museum, while Hunter, due to a curse which prevents her from entering London Above, remains in the abandoned British Museum underground station. After some searching they find the Angelus, which Door "opens" using her family's Talent, and travel through it to the underground home of the angel. Islington explains that his position as protector of London Below is a punishment for the submersion of Atlantis, which was also under his care, and tells Door that he will help her learn the identity of those who killed her family, for a price. She and her company must retrieve a unique key from the Black Friars and bring it to the angel.
The two return to the Museum and go below to reunite with Hunter. In the meantime, the Marquis seeks out Croup and Vandemar, exchanging a priceless Tang dynasty figurine for information regarding who ordered the murder of Door's family. The true price for this information, however, is his life; Croup and Vandemar capture, torture, and kill him, breaking the one-hour "head start" agreement that was part of their deal with the Marquis.
Door, Richard, and Hunter proceed onward to the dwelling of the Black Friars. There, they are faced with a series of three ordeals; Hunter wins a test of strength, Door wins a test of intellect, and Richard, alone in history, wins a test of character. He was convinced his adventures Below had all been a hallucination, but a trinket from his now-dead friend Anaesthesia re-orients him. As a result, the three succeed in gaining the key. Richard's ordeal greatly changes him, causing him to lose most of his self-doubts; he is now confident enough to interact with other beings of London Below. The three then travel to the Floating Market, where they are unable to find the Marquis, but where Hammersmith, a blacksmith friend of Door's is able to secretly forge a copy of the key won by Richard. Richard enlists the mysterious Lamia, one of the vampire-like Velvets as a guide to the angel's residence.
They travel on London Below's Down Street, toward Islington. Door, Richard, Lamia, and Hunter make their way down the long path of Down Street. Meanwhile, the Marquis' body is found on a Market and revived by Old Bailey, who uses the box containing the Marquis' life. Weakened, the Marquis sets out himself, following Door and company. On Down Street, it is discovered that Lamia was a dangerous choice for a guide, because the price she demands of Richard for her services is higher than he can pay and yet live, but the Marquis appears in time to save him.
It is also discovered that Hunter long ago turned traitor to Door's cause. She gives Door to Croup and Vandemar, in exchange for the magical spear she needs to hunt and slay the great Beast of London. Croup and Vandemar, with Door captive, travel downward, while Richard, the Marquis, and Hunter travel at a slower pace, all toward the great labyrinth through which they need to pass to reach Islington. In this labyrinth the Beast of London dwells. Hunter and Richard battle it, with Richard being the only survivor.
Richard and the Marquis rush ahead, to the final confrontation between the parties, in which Islington's true nature is revealed. Islington wishes to use Door and the key to force open the door to Heaven, where he seeks dominion over all the other angels as revenge for his banishment. After Richard is tortured by Croup and Vandemar, Door agrees to open the door, but she uses the copy of the key Richard won. The key does not open the door to Heaven, but instead to somewhere else, as far away as she could imagine. Islington, Croup and Vandemar are all sucked through the gateway before Door closes it. Door then uses the Black Friars' real key to allow Richard to travel back to London Above, where he finds himself restored to his normal life as it was before he first met Door.
After returning home, Richard is happy for a time, but he realises that his experiences have changed him, and that his old life and friends mean little or nothing to him now. He realises that he is not satisfied with the regular world, and wants to return to London Below but does not know how to do it. He despairs of returning, feeling that he has ruined his life about as completely as possible, but in the end the Marquis provides a way back.