This book will remind the Sci Fi readers among you a bit of "The Difference Engine" by Bruce Sterling and William Gibson, in that it is set in 19th Century England. But Mcleod has different obsessions: while containing elements of fantasy and alternate-History Sci Fi, the book is really about politics, ideology, and the comprimises people make in life.
The McGuffin (perhaps?) of the book is Aether, a substance mined from the ground that potentiates spells and incantations. Its used in fabricating items like bridges and steam engines -- after constructing a flimsy steam engine, the combination of incantations and aether makes it strong enough to use. It has unfortunate side effects for people who work closely with it, who turn into malformed creatures out of mythology.
The aether, at the time in the novel is running out, and at the same time a socialist revolution is simmering in the lower classes. The protagonist runs away from his family in an Aether-mining town after his mother turns into a sort of dragon, and becomes caught up in the revolution.
What keeps this book in my mind weeks after finishing it is the masterful quality of the writing, and the depth of the characters. Both sides of the revolution are depicted in the person of characters each with both virtues and flaws. And the aftermath of the revolution depicts a politics muddied by its collision with the real world.
I read science fiction for relaxation, primarily. Sometimes I do it so casually that I don't bother keeping all the characters straight. But "The Light Ages" had me engrossed beginning to end, and gave me lots to think about afterwards.