The novel opens with its protagonist, Susan, heading to an airport with her daughter to met her husband, Hal, and her employer, T. She doesn't yet know the tragedy that has befallen Hal at the end of Ghost Lights, but soon will (as much as I'd like to avoid spoiling that for you, it is said on the jacket of the book). Believing herself responsible for Hal's death, since it was his discovery of her infidelity that saw him leave the country, Susan is wracked with guilt, in a daze from mourning, and finds herself through a long lost uncle, the inheritor of a giant mansion full of stuff animals. The inheritance is a bit clumsy--Millet has had three books to layer the world of her protagonists and this is just a random plot device insertion--but it is serviceable. In addition, the house itself, sprawling across huge grounds with the trophies of dead animals hung upon the wall and a secret beneath the ground, does make up for the narrative laziness by the end of the book.
As I said, there is a lot to like about Magnificence. Millet's prose, as with the previous two, is wonderful, and her characterisation of Susan, a woman who has used sex to define herself since the accident of her daughter, is superbly done. Likewise, the narrative, in contrast to that of Ghost Lights, which just felt flat for its entirety, was interesting, engaging, and more than enough to make me read the book in two sittings. It also made Ghost Lights a lot better of a book, giving it more depth and more reach than it had while I was reading it. Magnificence does that with How the Dead Dream as well--in that way, in functions very well as a third novel--but to a lesser extent, possibly because of the connection that Hal and Susan have due to their marriage.
Having read all three in successive order, however, I have to say that my initial belief that all three narratives would have felt better layered upon each other as a novel has proved true. My one criticism throughout all three novels is that, isolated, none have enough substance to warrant being a single book. Magnificence is the only one of the series that you could argue has enough to be stand alone, but of course, it is the least stand alone of them all, since as the third, it is tying up narratives and bringing the thematic conversation of extinction to a close. In combination with the strong influence that it has on Ghost Light's narrative in particular, it becomes almost impossible to view it as a singular book. That, of course, isn't a problem--and in fact, makes me believe that Millet, had she decided to layer each narrative in one novel, would have had a superb book instead of three novels of varying success.
Such a complaint isn't a very fair one, however. Millet wrote and sold the books how she saw fit, and they are how they are, but I recommend, if you plan to read the sequence, just putting aside the time to read all three back to back.
It is best that way, I believe.