There are many ways to analyze plot structure in novels, plays and movies. The one I'm most familiar with are the Act/Scene/Beat breakdown taught by Robert McKee in his book Story and in his seminars.
Another, one that's probably a little easier for the neophyte, is the beat sheet shared by the late screenwriter Blake Snyder in his book, Save the Cat.
If you're interested in learning to plot better, you can't find a better place to start than with Snyder's book.
The table below represents Snyder's Beat Sheet, which assumes a 110-page script. I was looking at the trade paperback version of Twilight, which ran 498 pages. Because Snyder recommended that certain things happen at specific intervals in a movie script, I've listed the appropriate page numbers from the script and applied a multiplier of 4.54 to calculate a similar spot in the book.
Where Twilight varies from Snyder's recommended placement of a beat, I've indicated the suggested spot with a strike-through, followed by the actual page number(s). As you can see, up to about the midpoint, Meyer sticks pretty close to Snyder's beats, then blazes her own trail. Which is interesting, because it's that last quarter of the book that has all the action. It's relatively cerebral up to that point.
Also, Twilight doesn't really have much of a B story. For lack of anything better, I treated the "Bella settles in at a new high school" as the B story, but it doesn't get much page time.
Note: In a normal book/movie the A and B stories get switched when you move from the printed page to the screen. This is because the A story in a novel tends to occur too much inside the protagonist's head to translate well to the screen. The B story tends to be more action-oriented, which works a lot better for film.
|Script Page||Twilight Page||Beat||What Should Be Happening|
|1||5||Opening Image||Foreshadowing of James attacking Bella|
|15||68||Theme Stated||"That was the first night I dreamed of Edward Cullen."|
|12||55||Catalyst||Edward risks exposing himself as a vampire when he saves Bella from being crushed by Eric's van|
|12-25||55-114||Debate||Bella tries to figure out how she feels about Edward Cullen|
|25||114||Break into Two||Jacob tells Bella about "the cold ones" and Bella realizes Edward is a vampire.|
|30||136||B Story||Bella goes to Port Angeles with Jessica and Angela|
|30-55||136-250||Fun and Games||Edward rescues Bella from the rapists; he and Bella spend the day alone in the meadow|
|55|| ||Midpoint||Edward finally commits to not kill Bella (a high point in any relationship)|
|55-75|| 250- ||Bad Guys Close In||Rosalie doesn't like Bella; James catches a whiff of Bella and begins to hunt her|
|75|| ||All is Lost||James claims to have Bella's Mom hostage|
|85|| || Dark Night of the Soul/td>||Bella thinks about all the stuff she's losing as deliberately walks into James' trap|
|85|| ||Break into Three||Edward arrives to save Bella|
|85-110|| ||Finale||Bella and Edward go to the Prom|
|110||500||Final Image||"...and he leanded down to press his cold lips once more to my throat."|
Next week: Acts/Scenes/Beats (different kind) value changes and rising action.