» Sun Mar 27, 2011 9:33 am
Spoiler tags aren't working. Screw you, spoiler tags. In the old fashioned method then: warning - SPOILERS
Imagine that the film starts when Donnie's mother and little sister are in the plane on their way home. The engine is torn from the plane. This wasn't meant to happen. It is a disruption in spacetime, and so a Tangent Universe (TU) is created. The engine goes back in time to the actual beginning of the film. We are in the TU.
Donnie is the most affected by the engine (aka the Artefact) and so he becomes the Living Receiver. It is the Living Receiver's job to correct the spacetime corruption in the TU, righting the Primary Universe (PU). Being the Living Receiver grants you superpowers (I know, I was disappointed too) such as telekinesis and extreme strength - think of how Donnie buries the axe into the solid bronze statue.
People around the Living Receiver - but especially those who are to die in the TU - act oddly in the TU. The ones who die are called the 'Manipulated Dead', and they act in such a way as to manoeuvre Donnie - the Living Receiver - into a position at which he can use his superpowers to fix the spacetime corruption and end the TU, putting the PU back on track. Some examples of this are Ms Pomeroy telling Gretchen to sit with whoever she thinks is cutest, Gretchen warming to Donnie quickly despite him being awkward and strange, Roberta Sparrow pacing back and forth waiting for Donnie's letter (not particularly important in the normal edition unfortunately) and, of course, Frank's guiding of Donnie through the Fourth Dimensional Construct (http://www.donniedarko.org.uk/philosphy-of-time-travel/).
So yeah, basically what you have is a bunch of odd, dead to be people unknowingly guiding Donnie around until the end of the film when he stands at the ridge and uses his telekinesis to send the Artefact back into the PU. The loop is complete, the engine is in the PU and Frank has no need to save Donnie (indeed he can't, because we're back to reality now).
Also, people remember what happens in the TU to some extent in the PU. This is shown in the aftermath of the film when Jim Cunningham cries (remembering the shame of being exposed as a paedophile), when Gretchen waves at Donnie's mother (they must have become acquainted to an extent for Gretchen to go on Donnie's trampoline) and when Frank cannot sleep, and rubs his perfectly healthy eye (remembering both the guilt of running over and the pain of being shot in the eye by Donnie). However, nobody actually remembers the TU. They just experience abstract emotions. The most powerful example is Donnie's hysterical laughter before he goes to sleep - he is experiencing the euphoria of knowing that he's saved the world and the girl he loves.
It goes a bit deeper than that I think but once I found out that Donnie gets superpowers I became seriously disillusioned with the film.