I've developed an enthusiasm for OUP's Very Short Introduction series and accumulated a dozen or so of them, mostly on economics and science. Also a few from Princeton UP's science essentials series. They are great if you want about 200 pages on Marine Biology or Malthus, written by an expert professional.
Anyway, my current attention has focused on economics, starting with Keynes. Keynes is probably the dominating figure of Twentieth Century economics, a man of such intimidating intellect that even Bertrand Russell and Ludwig Wittgenstein were abashed.
Bertrand Russell has written that ‘Keynes’s intellect was the sharpest and clearest that I have ever known. When I argued with him, I felt that I took my life in my hands, and I seldom emerged without feeling something of a fool.’
Skidelsky, Robert. Keynes: A Very Short Introduction (Very Short Introductions) (p. 4). OUP Oxford. Kindle Edition.
The fight over his legacy continues 75 years after his death. The decades after his death were marked by an enthusiastic use of his method of stimulating the economy through deficit financing and unprecedented growth and prosperity, at least in the US. Few things, though, can fail like an excess of success and Keynesianism was inevitably applied at times when he had explicitly warned that it should not, and just as he predicted, it culminated in inflation, and as it happened, the dreaded stagflation of both inflation and unemployment. The reaction was Reagan, Thatcher, and a return to austerity.
While the inflation demon was vanquished at heavy cost, unemployment proved tougher, especially in Europe, and the whole "free markets regulate themselves" came crashing down in the Great Recession of 2007-2008.
I am currently reading: