Grout - A History of Western Music would be my first recommendation for a one book overview. There’s also the Joseph Machlis The Enjoyment of Music, but it’s more of a ‘music appreciation’ course sort of book, and it’s sounding like you want a little more depth… Beyond these, most books tend to focus on a specific period, composer, instrument, ensemble or style.
The ideal book of music theory hasn’t been written yet. While we wait for Godot, I have enjoyed using the Aldwell and Schachter Harmony and Voice Leading in two volumes. There is also the Walter Piston Mark DeVoto Harmony, but enjoy is not even remotely the word I would choose to describe working with it. He knows what he’s talking about, he just comes up with some of the most Proustian utterances to try to convey his meaning. If you want that sort of thing, there is absolutely nothing more thorough than the Arnold Schönberg Theory of Harmony. It, too, is very rough going.
For biographies of composers that focus on the composer’s style and composition, you might be best to go through something like the “Cambridge Companion to…” series, and follow up on their suggested reading. I’ve been following a series that does the exact opposite, that is to say, focuses on the biographic aspect and less on the composers’ music - the Illustrated Lives of Great Composers series published by Quantum Press. Groves has published some of their longer and more commonly searched articles as separate books - I remember ‘Piano’, ‘Beethoven’, ‘The Second Vienna School’, etc. being around the Toronto Public Library not that long ago.
Oh, while I’m thinking of that, you can subscribe to The Grove Online Dictionary of Music and Musicians, and it’s fantastic. This has reminded me - when I first got Sibelius 2, the music writing software, there was a free subscription for a year attached to it. Now that I’ve upgraded to Sib 5.x, I should check if that offer ever got repeated. It was great, it was just that the renewal came up at a time when I couldn’t afford it. It was great to be able to access Grove’s at the click of a mouse…
Hope that helps for a start.