He spends much of the book arguing that the proper way to interpret the Constitution is "original intent" -- the meaning that the framers of the Constitution had in mind when they wrote it. The way Bork does it is to bring up all the other schools of interpretation, and show flaws in each one of them. I will say that the flaws he points out are quite genuine. So, at the end, the only one left standing is original intent.
However, there are two problems with Bork's approach. The first is that there may well be another school of interpretation that he did not cover. I'm not saying that there is, nor do know what it might be, I'm just pointing out the possibility that Bork may not have covered all the possibilities.
The second problem is that one can subject original intent to exactly the same examination that Bork gave the other schools of interpretation. I did that -- Bork showed me how -- and guess what? Original intent has exactly the same sort of flaws that all the others exhibited. For example, it is not always clear just what the original intent of the framers was. They were a diverse group who frequently argued among themselves -- indeed, one can show cases in which an individual framer changed his mind. So how do you determine the intent of the framers. And, since they disagreed with each other, should one seek out the words of George Clinton or Alexander Hamilton? And what about Thomas Jefferson, who was in France during the entire Constitutional Convention?
Speaking of Jefferson, here is a germane quotation:
Some men look at constitutions with sanctimonious reverence, and deem them like the ark of the Covenant, too sacred to be touched. They ascribe to the men of the preceding age a wisdom more than human, and suppose what they did to be beyond amendment... laws and institutions must go hand in hand with the progress of the human mind... as that becomes more developed, more enlightened, as new discoveries are made, institutions must advance also, to keep pace with the times.... We might as well require a man to wear still the coat which fitted him when a boy as civilized society to remain forever under the regimen of their barbarous ancestors.