My understanding of copyright is that it applies to the idea too. If you change the names and wording but keep the plot of a novel, even if the text are not strictly identical, you could still be sued for breach of copyright.
If you "change the names and wording" you're actually copying and making a modification. However, if by pure chance you came up with some say detective story that has a plot very similar to one of the existing billion other detective stories, no can sue you unless there is sufficient evidence that you actually infringed a copyright.
Independent reinvention is a complete defense for copyright (you can't infringe copyright if you didn't copy), but not for patents (someone you've never heard of can sue you).
The courts are less clear on that. There's no statutory language that gives you copyright to the idea of a novel (which is dangerously close to genre if you ask me).