The classic explanation of Karl Marx's economic theories, by American socialist Ernest Untermann. The theory of historical materialism, the labor theory of value, the theory of surplus value, wage labor and profits, pre-capitalist societies, and the economic transition from feudalism to capitalism. Written for an audience of rank-and-file working people during the early union movement, "Marxist Economics" presents the most influential economic theories in history, in a non-technical way for non-economists.
If this author had spent as much time unpacking the Marxian labour theory of value as he had spent slandering the marginalists and Henry George, it might have turned out a half decent book. Rather than wasting money on this obselete book, I would recommend buying "A companion to Marx's Capital" by David Harvey or keeping the money and watching the videos by the Marxist youtube user named 'brendanmcooney', or visiting his Kapitalism101 wordpress blog. If you aren't interested in buying those books, don't be afraid to just tackle Marx head on. You will find he is surprisingly easy to understand compared to most 19th century thinkers.