Book recommendation on Keynesian economic theory?

A close friend of mine is enamored with Ron Paul and his libertarian message. In particular, he is enthusiastic about his call for a return to a commodity-backed currency and eliminating the Federal Reserve and IRS.

I’m looking for a book to give him that makes sound, economic counterpoints in favor of the Keynesian economic system. The book should be written in plain English, accessible to someone without a strong background in economics, and contain lots of concrete historical examples.

WARNING: Any off-topic, pro-Ron Paul comments will be flagged immediately.