So much has been said already about the plot, and the fact that its really just the end to the previous book that I won't say more here. My first point is that I agree with King's insight that a man like Mycroft Holmes, who has a shady job inside the government, may not turn out to be all ethics and morals. A man with such a job has to be extremely practical, and at times unethical. His "embezzlement" reminded me a great deal of the Iran-Contra affair in the U.S. Kudos to King for seeing that Mycroft would not just be this big and fuzzy, all knowing, wise teddy bear, as he is often portrayed by other authors.
Second point: I agree with other commentators that the villain in this story was weak and undeveloped. Actually, they both were (there really were two villains, one just killed the other). Reading other King books leads to the conclusion that she has a fascination with religious cults, which explained the direction of the first book in this two part series. However, this second book introduced an entirely new villain, and this book, though a completion of the last, went off in a completely different direction. I felt that this villain was just created and sketched in to provide some explanation for events King wanted to put Russell and Holmes through. The villains were not the only characters I felt were undeveloped. I agree with the critics who felt that Damian Adler was also woefully underdeveloped. I hope that will be remedied in later books.
Third point: The ending was very disappointing. I felt like she got to a point where she said, how can I wrap this up?, and she rushed to do so. I kept waiting for the moment when Holmes meets his granddaughter for the first time, but it never came. Holmes, suddenly thrust into the role of grandfather to this precocious 3 year old girl, would be a scene well worth writing and reading. Russell even hinted at it throughout the story. But then, nothing. Just some open packages and that's it. I even felt the scene on the bridge was awkward and undeveloped. So much seemed to be promised, and then it fell flat. I had the distinct impression her publisher called and said we need this tomorrow.
Finally, I have read criticism about Russell from readers who are not fans of the series. I find it ironic, though, that they keep reading the books. Although, perhaps I understand it. I, too, have found Russell grating. Part of Holmes' appeal was that, while he had some amazing qualities, he was also deeply flawed. We could appreciate Holmes' genius, but also feel that, in many ways, we functioned better than he did. He was human, in other words - a flawed, interesting man. Russell, grates, however, because she is always right, always smarter than everyone else, etc. King has tried to "humanize" her by making her poor at cooking, but that's a skill Russell clearly doesn't care about anyway. Being bad at cooking actually accentuates her superhuman feminist self. In this book, we do see her notice that she has missed some things Holmes has noticed, which helps to bring her down a notch, but not much. Since Russell is the primary narrator, she just comes across as a braggart. That's not a nice quality. Actually, I think, though, that it is consistent with her age and immaturiy. She thinks she's so mature, and mature enough for someone like Holmes. However, she reveals herself to be no more mature than other women her age. One can only think Holmes keeps her around to do his dirty work for him, since she is relatively intelligent and willing to do whatever he tells her to do. (Which also suggests she's not quite the independent spirit she thinks she is.)
All said, if you haven't read the books before, don't start here. Read the others, and if you like them, and they hold your attention, keep reading. All in all, King can weave a good tale. She has moments of genius, but then, I think, she just gets bored and tired, and rushes through.