The book has four core arguments. First, rational expectations theory, as a methodological but not descriptive assumption, is the friend of Austrian Business Cycle theory, not its enemy. Second, classic Austrian Business Cycle theory is not tenable (more on this some other time; the basic argument is that ABC requires an excessively particular theory of how individual investors err). Third, the theory should be refocused around the category of risky investments, thereby leading to a viable synthesis of Keynes and Hayek. Fourth, there is some (non-decisive) empirical evidence in favor of such a synthesis.
Here is my previous post on Austrian Business Cycle Theory and its relevance for current events.