The Philosophy of Time Travel · Chapter 10
The Manipulated Dead
Frank and Gretchen both die inside the Tangent Universe, which makes them the Manipulated Dead: able to travel through time and contact Donnie through water. Frank's countdown, his instructions and Gretchen's death are the Ensurance Trap that guarantees Donnie returns the Artifact.
The Manipulated Dead are more powerful than the Living Receiver. If a person dies within the Tangent Dimension, they are able to contact the Living Receiver through the Fourth Dimensional Construct.
The Fourth Dimensional Construct is made of Water.
The Manipulated Dead will manipulate the Living Receiver using the Fourth Dimensional Construct (see Appendix A and B).
The Manipulated Dead will often set an Ensurance Trap for the Living Receiver to ensure that the Artifact is returned safely to the Primary Universe.
If the Ensurance Trap is successful, the Living Receiver is left with no choice but to use his Fourth Dimensional Power to send the Artifact back in time to the Primary Universe before the Black Hole collapses upon itself.
In the film
Frank
Frank dies on October 30 when Donnie shoots him through the eye. Because he dies inside the Tangent Universe he is able to reach back across the whole of it: the Frank who wakes Donnie on October 2 is the Frank who is already dead on October 30. That is why he knows the exact time the world will end, why he wears the costume he was wearing on Halloween night, and why the bathroom mirror ripples like water when Donnie touches it.
The Ensurance Trap
Frank's instructions across the 28 days (flood the school, burn the house) set in motion the chain that ends with Gretchen killed by Frank's car outside Roberta Sparrow's house. With Gretchen dead and Frank shot, Donnie drives to Carpathian Ridge and sends the Artifact back - in Sparrow's words, he "is left with no choice but to use his Fourth Dimensional Power".
Gretchen also dies inside the Tangent Universe, minutes before its collapse, and so is a Manipulated Dead too.
Where this chapter happens on screen.