I don't know exactly what it is you need explaining... The philosophy behind it? The actual physical plot itself? Well, regardless, Donnie Darko is a spectacular "cause and effect" film. Basically, it all starts when Donnie is dragged out of bed, while in a subconscious sleep-like state, by Frank, who is implied to be a mere product of schizophrenia. Now, I think what's really interesting is, there is actually a deleted scene that reveals Donnie is not a schizo, and that he is actually being fed placebos. However, I sort of prefer they kept that out, as it allows the audience more room to breath, and analyze the film for themselves.

Now, back to where I was going. When Donnie is pulled out of bed, a jet engine falls directly on his bed, as you know. The serial codes are burned off, and there are no reports of a crashed aircraft. Anyways, feeling as though he owes Frank his life, Donnie feels obligated to do as he tells him to do, which leads to a series of whacky events. And of course, time-travel kicks in when Frank asks Donnie about it, and Donnie feels as though he is to look into it.

But here is what interesting. When you think about it, all of the bad that happens in the film (The firing of the English teacher, the arrest of the motivational speaker, the death of the girl friend, the death of Frank, etc.) is a direct result of the actions Donnie makes because of Frank. At the end of the film, it's revealed Frank is a guest at Donnie's party, who Donnie winds up killing. Coincidentally, Frank is also the boyfriend of Donnie's sister. But, the whole thing about the end, as Donnie gazes out over the mountains beside his dead girlfriend, and sees a time portal emerging in the sky, I think he seems to realize he could prevent all the pain he's created if he just gave himself up.

Then we're brought back to the very beginning of the film. Donnie is in bed, awake, and laughing--in the commentary, director Richard Kelly explains this is because Donnie is under the belief it was all just a dream. But I think in some subconscious way, Donnie still knows that he has to die. So he ignores Franks calls this time around, and lays in bed to die, thus saving the town of Middlesex from his "fear" as Patrick Swayze's character would have said. The jet engine fell off of his mother's plane in the future, fell through a time portal, and landed on Donnie's bedroom--thus the reasoning behind why no crash is reported. Donnie dies, and others are freed, for better or for worse.

In the end, it would seem as though Donnie is a Martyr.