Aquinas 101, by Francis Selman, is subtitled “A Basic Introduction to the Thought of St. Thomas Aquinas”; and that’s a pretty good description.

Most of the books I’ve read about Thomas have focussed on his philosophy and natural theology, e.g., his proofs for the existence of God and of God’s attributes, as accessible to reason. This one covers that, but then goes on to cover the remainder of his theology as well. It isn’t a long book, only about 200 pages, so the coverage isn’t deep; at least, I found the opening chapters on the existence of God to be rather shallower than other books I’d read. But on the other hand it covers the waterfront, which is a really good start. It helps to study the map before putting on your boots and going for a hike.

So, recommended, with caveats.