After a major-power war, the winning side sends an expedition to reinforce a new colony on an extra-solar planet. When they arrive, it seems that something has happened to the original colonists.
The reinforcing expedition has little in the way of weapons to deal with the newly discovered threat and the captain of the ship delivering them obstructs the colonists at every turn.
One of the two viewpoint characters is a discharged military hero, who takes up the challenge of investigating the situation, and eventually of resolving the problem. His character is well-drawn, with a complex personality and background. Once the story starts, while he is the primary driver of the plot, he doesn't change much. The other viewpoint character, his wife, has less screen time and a less-developed background, but is the more interesting character, with her relationship to the developer of the colony AI and need to overcome more personal challenges.
The setting is a bit sketched in, with the history on Earth more mentioned than explained and the situation on Tranquility left mostly to the combat scenes in the book. The ship that transports the colonists to the new system takes almost three years to arrive, which can't really be sublight (no time compression is mentioned), but also no super-light system is discussed either.
The details of the combat are evocative and well-paced, but there isn't much tactical complexity to the combat scenes that take up the majority of the book. The primary combat is undertaken by what are on the border between powered armor suits and mecha. The colonists have to make do with powered assist suits that have been modified to be field expedient suits. (Think "Bob Semple tank", frankly.) This probably works better than it should, but the suits are definitely at a disadvantage to the few remaining combat suits on Tranquility.
For my taste, at least, there's too much time spent on close combat between combat suits that result from frontal attacks by one side or the other. I'd rather have seen more effort spent on the world, the technology, and tactics than descriptions of blow-by-blow fight scenes.
I suspect this book will work better for other audiences, but for me, it was just OK. I'm not generally a fan of mecha, and while I like MilSF quite a bit, this didn't engage some of the complexities of the books in the genre I like better. If you're a mecha fan, this is done quite well; there are good reasons for the existence of at least the colony powered-assist suits and the conversion mostly makes sense. As it is, I'll read the next book eventually, but I have other priorities now.