By Light Alone was not quite what I expected. From the cover, I was vaguely expecting something futuristic and steampunk-y, an impression backed up by its blurb. In a world in which humans can photosynthesise with their hair, a new underclass has grown up, an underclass owning nothing and fearing nothing. The rich eat to flaunt their wealth, and there is talk of revolution among the longhairs.
Against this background of political turmoil, a child is kidnapped from a rich family. The novel follows the ripples that this kidnapping makes among the child's family and ties it (rather impressively) to the wider politics of this world.
It was...interesting. It reads like literary fiction - like Sebastian Faulks, or Ian McEwan - in a world not unreminiscent of Julie Bertagna's Exodus. Not exactly what I was expecting. Emotionally complex and politically engaging. I don't have any specific complaints, but I didn't like it enough to give it four stars...but, definitely, worth a read if you fancy some intelligent SF.