The world Donnie and those around him have been living in since the night the jet engine fell on his room is infact a 'tangent universe,' a parralel universe that branched of from the 'primary' universe when Donnie was saved from death by Frank. The 'end of the world' that Frank predicted is infact the date that the tangent universe will collapse, as it is very unstable and can only exist for around 28 days. On the final night before the universe collapses, Halloween, Donnie is compelled to go to Grandma deaths house with Gretchen, They are attacked by the bullies and Gretchen is eventually killed, hit by a car that swerves to avoid Grandma Death. Donnie, shocked, watches as the person driving the car gets out. It is Frank. He is a normal teenager, the disturbing bunnie suit nothing more than a sick holloween costume. Donnie takes out his handgun and shoots Frank is the eye, killing him. He takes Gretchen's body to the top of the hill where the film started and watches as the tangent universe begins to collapse. He sees a plane (that so happens to be carrying his mother and sister) lose a jet engine, and watches as it spirals towards what appears to be a wormhole. The universe collapses and we are sent back to where the film began, at the point where the tangent universe seperated form the primary universe. Donnie, laughing, willingly decides to stay in his bed and is killed by the jet engine as it falls and crushes him. In doing so, he has finally stopped the creation of the tangent universe, saving the lives of Gretchen, Frank and presumably his mother and sister. Donnie realised that his greatest fear of "dying alone" was his predetermined 'destiny' of sorts. The final scene is Gretchen, alive and before she met Donnie, watching from across the street as the authorities remove the jet engine from the Donnies room. She sees the Darko family, greiving over Donnies death and shares a wave of apparent recognition with Donnies mother, despite the fact that, in this universe, they have never met.