A Gleam of Light has many of the elements of a first-rate thriller: a sympathetic protagonist, mystery, conflict, and a fascinating backdrop. It's clear that a great deal of thought and research has gone into this book. These elements, however, need to be put together differently to keep the reader really turning its pages.
With respect to the characters, Una Waters is an appealing heroine. The deaths of her parents and her estrangement from her ancestral tribe and lands give the potential for a very moving character arc as the story unfolds. Unfortunately much of her backstory is "told" rather than "shown," as are the revelations that this or that plot development "changed her life." Colin and Jack are also intriguing characters, but are underdeveloped in various ways. I'd like to know more about Una's unfinished business with her childhood friends, her life in DC after her parents were killed, and how Colin rose to the rank of general at such a young age (if he was a bratty child on the opening plane flight, he couldn't be much older than Una herself). In general I wanted to know what Colin and Una saw in each other. In over 300 pages I didn't get a good sense of what any of these characters really looked like, let alone what specific mannerisms of speech or behavior they might have as adults.
In addition to those three main characters, there are just too many secondary characters in this book to keep track of. Many have unusual names, and they surface briefly only to disappear again for long stretches, or forever. The archaeologist seems to exist only to provide info dumps about tribal cultures and UFO sightings. And this may be just personal taste, but I don't need to see the "surprisingly precocious genius child wows adults with unexplained alien knowledge" trope in SF ever again. Or if I do, it needs to come with a really unique twist, which it doesn't here.
This book opens with "You have to believe in gods to see them." --Hopi proverb. I'm a skeptic by nature. I don't watch the X-files and I am impatient with conspiracy theories. That being said, I enjoy reading and watching Science Fiction and Fantasy, and I am happy to suspend my disbelief to immerse myself in a well-imagined, well-written fictional universe. In order for the universe in this book to function that way for me, it needed more suspenseful plotting and a more climactic ending. It also needed to integrate the authors' painstaking research more seamlessly. Instead, its tone and setting waver unsatisfyingly between gray realism and New Age spaceyness. I am an outsider to Hopi culture, so I trust that the research and cultural anthropology in this book are authentic, but I don't know if that is the case. I became more confused and overwhelmed than awestruck by everything that was discovered during the journey into the cave. This material might make a better screenplay than novel, because I got the sense that the characters were seeing something that I wasn't. I also didn't understand why the main events of that journey had to remain secret at the end, except that this is the first book in a trilogy. This is a worthy effort but the authors may have bitten off a bit more than they can chew.