The genius of Clancy's story, its basic believability, like Tolkien's, comes from a firm commitment to letting the plot unfold logically once the initial hook is in place. It is perhaps difficult to believe there is a ring of power that confirms upon its bearer numinous strength, or that a Russian missile submarine commander, in charge of the newest and most secret sub, would defect along with all his officers. But once you buy the beginning, the rest of the books proceed with rigor.