Alright...check this out. I discussed this with a guy I know who has read the book. He explained it rather well. I'll do my best to tell it you guys. Time is constant. However, when something passes through the portal, aka the jet engine, it creates a rip in time and an alternate world is the result. The alternate world only lasts a few weeks though. In the alternate world, there is a chosen one, the manipulated living and the manipulated dead. It is the chosen ones job to direct whatever caused the rip back through the portal. So Donnie's job is to direct the jet engine back through the portal. However, he dosn't know that in the beginning. That's where Frank, the rabbit comes in. The manipulated dead are people who die in the alterante world. They have the ability to communicate with the chosen one and direct them to the ultimate goal of fixing the rip. Frank is part of the manipulated dead. Throughout the movie, he instructs Donnie to do things that cause all the chaos. Flooding the school, burning the house down, etc. The manipulated living set up opstacles for the chosen one. The teachers and Patrick Swayze would be the manipulated living. Like the science teacher that Donnie talks to about time travel. So ultimately, Frank gets Donnie to do a bunch of fuked up shit so Donnie would create nothing but chaos and sees what happens when he lives. The teachers set up obstacles that allow Donnie to figure out his powers of being the chosen one and figure out what he's supposed to do with them. So at the end...Donnie goes to the cliff and re-directs the jet engine back through the portal which sends him back 28 days earlier where the engine kills him and the rip is fixed. Any questions??