This is an ongoing series, but these four books, the first four, constitute a unit. While there are climaxes, there are also a number of threads carrying over. Salute the Dark ties up the story threads, though there is still plenty of room in the world.
And an enormously complex world it is. Scads of races -- the Beetles, the Ants, the Wasps -- all human, and able to interbreed even, but enormously different in looks, and possessed of differing Ancestral Arts. Ants can talk mind-to-mind. Wasps have stings. Etc. Some races are magical (at least most of their members are); some races are Apt (again, at least most members) and can do machinery. Once they discovered that, a few centuries ago, an industrial revolution overturned the ancient order of the world. Thus combining the two tropes I probably like least about fantasy: the special gift needed to work magic, and the science vs. magic antithesis. The magically gifted have difficulties opening latches. . . . Still, the world is magnificently built.
In it, Stenwold Maker, a Beetle, having seen the fall of one city to the new, and rapidly expanding, Wasp Empire, is trying to preserve his own city, Collegium. Not exactly helped by the denial of its denizens. He has become a spymaster, and an intriguer, and when the Wasps move in the opening of the book, four of his students -- include his niece and his ward -- leave the city in his intrigues.
They are soon parted. And there are many other characters with POV, because this is a massively complex plot. Featuring long-lost fathers, and gladiator games, a powerfully magic box, intrigue and infighting, pitched battles, last-minute rescues, a sorcerer of a race thought dead, a paranoid emperor, aircraft, and much more. A good number of people die, especially in the last book.