John McWhorter's Our Magnificent Bastard Tongue: The Untold History of English
I actually listened to this book as an audiobook, read by the author, which made it even more enjoyable because he was a very enthusiastic reader!
You are probably aware of how English has borrowed words from many languages, but McWhorter wants to focus on the history of English grammar, the way we make sentences (and make meaning) with the words that we have: "The pathway from Beowulf to The Economist has involved as much transformation in grammar as in words, more so, in fact, than in any of English's close relatives. English is more peculiar among its relatives, and even the world's languages as a whole, in what has happened to its grammar than in what has happened to its vocabulary."
So, if you want to get a sense of the amazing rules you have in your head and that you apply with every utterance you make, this is a fun book to read!