Lizzie Collingham's Curry, A Tale of Cooks & Conquerors reads more like a college history text than an entertaining retrospective of curry. It's actually a lot more of a historical tome of India and the country's culinary influences than anything close to a focused book on curry.
I learned much more about India and its cooking styles than I expected. I also gained a greater insight into how bastardized "Indian" food became after the British took hold there.
Just a warning, Curry isn't light reading. It took me several months to get through it because when I read, I either read cookbooks, Ruth Reichel's books, anything by Alexander McCall Smith and foodie magazines. When I spend your day thinking, writing and analyzing, the last thing I want to read is something that taxes me. So, if you're like me, and determined to try something new, just be prepared to chip away at this one.