A guide in two parts. The first describes and discussed theories of economics, enumerating 9 of them, with their good and "bad" points. The point is very clearly made that there is no over-arching theory of economics, rather we have to use whichever one seems to best fit the situation, so that economics isn't as clear-cut a "science" as physics. (Though the author misses the chance to point out that physicists think of light as being both particles and a wave form, depending on what's happening.)
Science usually goes from observations to a theory, and from there to constructions based on the theory that can be tested; these may tend to confirm or refute the theory. By contrast, economics seems to the outsider to be based on pure theory, more akin to thinking how things ought to be rather than how they actually are. If Chang explains why this isn't the case, then I missed it. And the outside thinks that ideas like "perfect" competition, markets etc, seem to be a gross oversimplication.
The second part is rather different; it's not so much about "economics" as "political economy", and the point is well made that economics cannot be seen as something pure and unsullied, rather it is always connected to politics. There are some discussions about the blunt application of theory and the disastrous consequences that have occurred by blind adherence to a particular theory.
I'd have found it useful if the 9 theories had each been applied to a few scenarios, either real or imagined, to see what the outcomes could have been otherwise.
The messages are: it's really "political economy", and that no single theory is adequate to explain everything. But quite how to choose the most appropriate one for the particular circumstance remains out of my grasp.