Having adored Weeks' Night Angel series I was surprised that it took me a while to get into this. I put it on one side, almost stopped reading, and then came back to it after a couple of months. Reasons for putting it aside included not being able to feel much empathy for the main characters... but that changed as the book progressed. .OK, from the beginning. This is a world of magic and the magic system is complex and well thought out. Drafters use light to draft coloured luxin that can have different properties, temporary or permanent. Most drafters can handle one colour, some can handle two, but Gavin Guile is the Prism, who can handle all the colours at once, which makes him tremendously powerful. He's nominally the 'emperor' figure, but not quite as grand as he eschews sitting in his ivory tower for being a hands-on prism, sorting out problems in the satrapies. The Chromeria - the governing guild which rules the drafters from training to their 'freeing' - is presided over by 'The White' and between them the White and the Prism are the head honchos of the magical fraternity. Unfortunately the more a drafter drafts, the closer he or she gets to going bonkers and turning into a colour wight. Before they get to that stage drafters are expected to volunteer to be 'freed'.
We pick up the story some fifteen years after a war between Gavin and his brother Dazen (the False Prism's War) which laid waste to a fair amount of real estate (and people), but Gavin is trying to put things right and turn things around. He doesn't have much time left. A prism doesn't usually last more than 21 years and he's had 16 already. He has goals for his final years (but we aren't party to them).
It turns out that in the heat of battle (well, maybe not during the battle, but you get what i mean) Gavin fathered a son and is now introduced to his 15 year old bastard, Kip, a potential drafter. There's something slightly awry (but we don't find out what until later in the book and no spoilers) however Gavin duly accepts Kip and sends him to be trained at the Chromeria as his... nephew.
It's a sprawling plot involving an uprising and a battle. There's tension between Gavin and Karris (his ex fiancee) who is also a super-soldier. Kip's point of view is on the point of being amusing as we get insights from his fifteen year old viewpoint. There's a reveal part way through the book that suddenly makes Gavin's character much more complex.