This is the second volume in Sean Carroll's "Biggest Ideas in the Universe" series. I reported on the first one, Space, Time, and Motion here.
My comments there apply, more or less, to this one: (1) There's a lot of math (and Carroll kind of assumes you've mastered the classical topics, like the Langrangian and Hamiltonian); (2) Like the first book, I got lost at many points, finding myself totally out of my depth. Although (good news) I was often pulled back into more accessible territory.
The basic idea is simple enough to express, even when you don't really understand it, can't visualize it, don't get the math. At bottom, just about everything is a "quantum field" of one sort or another. What we experience as particles, working their way up to atoms, molecules, etc., are excited states of those fields. This is easiest to describe with electromagnetic fields, which (when poked) produce photons.
I liked his description (it's near the end) of why we experience (some) matter as solid. When most of the "space" in an object is taken up by very unmassive electrons, why don't we (for example) just fall through the mattress when we hit the hay at night. Or fall through the floor when we walk to the bedroom. Or fall through the earth's surface and, … well, you get the idea.
The answer is a "force" that's not one of the Big Four Forces you heard about as an undergrad (gravity, electromagnetism, strong and weak nuclear). It's the "Pauli repulsion" force, brought about from the fact you can't have two electrons in the same quantum state. And Carroll explains that, if you'd like.