Blackshirts and Reds. It covers some very important history, illustrates how capitalism decays into fascism and is destroying us and the planet (and has done so in the past), introduces some baby steps into Marx at the end of the book, and debunks many anticommunist talking points. Also it's more modern writing so the lib can actually understand it without a dictionary in the other hand, is quite funny at points, and hits them with the emotional punches they need. I cry every time I read it.