Response from my boyfriend, who studied music at uni:
Well, there's the Oxford "A Very Short Introduction to Music". That will give you a certain amount of history. What kind of theory did you mean? Analysis is easiest by buying CDs from Naxos and reading the sleeve notes. The best way to learn theory is actually by doing the exercises, so the analogy with popular science books doesn't actually quite work.
(I'd disagree with him there, actually, as the best way to learn science also includes actually doing some, but popular science books are not intended to teach you in the same way as you would for someone who actually wanted to learn properly.)
Popular music theory
Well, there's the Oxford "A Very Short Introduction to Music". That will give you a certain amount of history. What kind of theory did you mean? Analysis is easiest by buying CDs from Naxos and reading the sleeve notes. The best way to learn theory is actually by doing the exercises, so the analogy with popular science books doesn't actually quite work.
(I'd disagree with him there, actually, as the best way to learn science also includes actually doing some, but popular science books are not intended to teach you in the same way as you would for someone who actually wanted to learn properly.)