[I'm having a huge problem writing this review, because every time I pick up the book to check a name or remind myself of a plot point, I find myself reading another chapter or two. And The Mirador, third in the sequence, is imminent, if Amazon's delivery estimate is to be believed ...]
Mélusine (a place, not a person, despite my initial assumption that it'd feature a serpent-woman) has two first-person narrators: Felix Harrowgate, a court sorcerer, and Mildmay the Fox, a cat burglar and assassin. Both are intriguing characters, but where the novel really takes off, for me, is when the two meet.
That encounter isn't as straightforward and predictable as it might be in a typical quest fantasy with its carefully randomised selection of characters from Central Casting; but Mélusine is not, in any way that matters, a typical fantasy. Both Felix (whose persona of aristocratic magician is deliberately shattered in the first few pages) and Mildmay (who might conform more closely to the 'lovable thief' archetype if his voice wasn't so distinctive, and his doubts less internalised) have unpleasant secrets in their pasts. That they are secrets until Monette chooses to reveal them -- without there being any sense of gaping voids in plot or characterisation -- is assurance enough that we're in safe hands.
Felix is used as a weapon and sent mad by it: Mildmay, meanwhile, falls in with a shopgirl with aspirations named Ginevra, and ends up crossing some people it'd be best not to cross. Both Felix and Mildmay end up leaving Mélusine for their health: Felix disturbingly, vividly, credibly insane and prone to seeing animal-headed monsters; Mildmay in the company of a crippled sorcerer and his unsociable henchman Bernard. Also, there's the slight matter of the fire consuming the city ...
Given the title of the novel, it's surprising that so much of the action happens after the characters have, effectively, exiled themselves from the city. Mélusine is a richly-detailed metropolis, saved from sprawling by immense walls, where cathedrals soar above dark and nasty alleyways; where multiple gods, saints and darker entities are worshipped or placated; where two calendars are used; where ghosts and ghouls are physical dangers after dark, or in the wrong place; where there are more 'wrong places' than one might expect. This is not our world, but the names of streets and suburbs have familiar echoes: Rue St. Bonamy, Plaza del'Archimago, Catacombes des Arcanes. The history that Felix and Mildmay know (which Monette surely knows in extravagant detail, though it's referenced only in passing) mentions Troians, Kekropians, Merrows. And, incidentally, there are alligators (as well as nastier things) in the swamps.
All of which inclines me to view this as a very American fantasy, with a melting-pot of cultures and history and a certain flexibility about social class (Felix goes slumming; Mildmay, while not a habitue of the Mirador, is perfectly capable of scrubbing up nice and being bored in middle-class bars.)
There are flaws. At points (especially, but not exclusively, before Felix and Mildmay meet) the plot seems somewhat episodic: a trial is overcome, and along comes another trial. Later, some of these events do join up and assume greater significance. Not all of them, though, so the effect is occasionally of a series of swashbuckling episodes adrift on a dark and roiling sea of myth, metaphor and magic.
And that episodic feel leads me nicely to another kind of flaw, which is that it wasn't at all clear that Mélusine was first in a series -- a series, in fact, in which the second novel (The Virtu) leads on more or less directly from its antecedent. Having come late to Mélusine , I picked up an edition with the first chapter of The Virtu as endmatter: it would have been extremely frustrating if the novel had just stopped without indication of more.
This review might be rather longer if The Mirador (third in the series) had not just arrived. Which should give you an indication of just how hooked I am.