It reminded me a lot of Dr. Who, which I don't like, but it was interesting enough for me to finish all six episodes last night. Richard Mayhew (reminded me of Joe and his whimsical signature) works at a good job in London. He's engaged to a woman named Jessica who works at the British Museum. We find out immediately how she feels about herself -- both she and Richard have pictures of her on their desks. No picture of Richard on hers. As they head to dinner with her boss, a knived young woman falls onto the sidewalk in front of them. Jessica tells Richard she'll break their engagement if he helps the girl, and he does anyway.
A couple of guys claiming to be the girl's brothers come looking for her, and Richard has the sense to tell them he's never seen her. As she heals and leaves, he finds that nobody in London can see him anymore. He fills a duffel bag with what he really needs and tries to get money from the ATM. It doesn't recognize the card, but a man comes up who can see him. The man takes him through a wandering course to London Below. Turns out there's a lot going on down there.
From here, he becomes a companion and champion for the girl and there's lots of odd characters and so forth. The actors are much better than usual in this kind of show.
There's a lot of double-meaning (the poster of Angels Over London is everywhere) and plenty of symbolism. I lost the first one, though -- the first episode is "Door" and the girl is Dor. At least, that's what I was thinking (Little Dorrit) until I saw the cast list.
If you like Dr. Who or similar, you'll like this.