So I'm assuming you mean the one everyone talks about, that specific 'London novel.' If it's the one about the shadowy, alternate-history city with the sentient Thames and the guy who can talk to bridges, then yeah, the protagonist is a weirdly quiet civil servant named Arthur. He's not your typical hero at all, just sort of stumbles into this whole hidden world because of a bureaucratic filing error. I found him kind of frustratingly passive for the first third, but the way he grows into his role, learning to negotiate with the spirits of railway stations and such, ends up being the point. The book’s more about London itself being the main character anyway, with Arthur as our bewildered tour guide.
Arthur's relationship with the river spirit is the real heart of the story though. It starts off as pure business, him just trying to stop the Thames from flooding the financial district, but it becomes this oddly touching friendship. The ending, where he has to choose between the city's old magic and its new bureaucratic order, still sticks with me. He makes a choice that feels sad but right, which fits the melancholic, grimy-but-beautiful vibe of the whole thing.