I bought all four of qntm's books when I discovered the fantastic There is no Antimemetics Division. I didn't really expect to like all of them, sight unseen, but was delighted to support an emerging author who had contributed to the genius of SCP. But then the books that arrived turned out to be bloody brilliant.
This one tells a tale in which magic was discovered to be real in the 1970s, becoming a new, arcane branch of physics. From there, it piles on the twists and raises the stakes at an enthralling and dizzying rate, demanding the reader to keep up through many exciting layered reveals and escalating changes of perspective. Absolutely smashing.
Like Antimemetics, it scores points with me for including some female heroes, who surmount challenges through some striking strengths of character & expertise, rather than simply being the best at applied violence.
For those like me with an epub fetish, you can buy Ra in many formats, including Amazon links, EPUBs, or free-to-read online, at the author's site.