I understand that ideas cannot be copyrighted, but stories can be....but I don't really get it. If I copied all the plot in a story but wrote it in my own words, wouldn't that just be taking an "idea"?
An "idea" cannot be copyrighted, but an "expression of an idea" can be. "Boy meets girl" cannot be copyrighted, but "Romeo and Juliet" can be. If the plot is a generic plot, it cannot be protected -- but a very detailed and unique plot probably can be. There are other things that cannot be fully protected, even in a detailed plot, specifically
scenes a faire; Wikipedia has a good example of this:
"For example, a spy novel is expected to contain elements such as numbered Swiss bank accounts, a femme fatale, and various spy gadgets hidden in wristwatches, belts, shoes, and other personal effects. These elements are not protected by copyright, though specific sequences and compositions of them can be."
http://en.wikipedia.org/wiki/Scenes_a_faire
As noted in another one of your threads, this is all a "grey area" -- whether you are using the noncopyrightable "idea" or copying the copyrightable "expression" is a factual question that can only be determined, if at al, by a careful review of all of the specific facts of your situation. There is no "bright line" rule that says "this is okay" or "this is not okay" -- its a judgment call based on a review of all of the facts.