I'm a huge Neil Gaiman fan, it's only natural that one of his rare forays into the world of television becomes an essential.
Richard Mayhew has a good job for a respectable London firm and a slightly overbearing fiancée. On his way to a dinner appointment with his fiancée and her boss, he finds a badly-injured girl, and being the good samaritan he is, gets her safely out of harm's way. In this case Harm comes in the form of The Old Firm, oily Mr Croup and the frankly absolutely mental Mr Vandemar, professional killers who've been taking on contracts for a long, long time (one of their biggest claims to fame is burning down the city Troy during the Trojan War). They are on the trail of the girl Richard saves, the Lady Door, who has the power to open and unlock absolutely anything. Croup and Vandemar, having butchered Door's entire family, are anxious to find her to fulfil their contract.
The Old Firm are the least of Richard's worries, because soon after Door leaves, he finds out that people don't notice him...and that it's almost as if he doesn't exist. He no longer has a job, or a flat, so goes looking for Door. He is drawn into the dark and dangerous world of London Below...
Instantly recognizable as a BBC sci-fi/fantasy production, on a par with Dr Who and Red Dwarf, and has the same inventiveness, considering the Beeb couldn't have given them much money to make this. Neil Gaiman's writing is wonderful, playing clever word games with London locations (we find out, for example, that there really IS an Angel Islington). I've visited London several times, and often wondered about the place names, like if there really are Shepherds in Shepherd's Bush (according to The Marquis de Carabas there are, but meeting them is not advisable).
Neverwhere is an excellent dark fantasy series that turns out suspense, drama and black humour on a bugdet of fourpence. One can only imagine what it would have turned out like with a Hollywood budget.