Doctor Who: Doom of the Daleks
The Daleks believe they are the superior race in the cosmos. All other life forms are equally despised. All other life forms must be exterminated. The Daleks make no distinction between Human and Ogron, between Silurian and Draconian, Ood or Sontaran. All are equally hated. All must be destroyed. Oh, there may be short-term tactical variations – exterminate the human enemies before exterminating the Ogron slaves – but that does not mean the Daleks hate the Ogrons any less than they hate the humans. All non-Dalek life is abominable. All non-Daleks must be exterminated. There’s only one exception. There is only one lifeform in the universe, in the entirety of time and space, that the Daleks hate more than any other lifeform.
The Doctor. The Predator. The enemy of the Daleks.
When the Daleks went to war against the Time Lords of Gallifrey for mastery of time, the Doctor was their most important target. On him they lavished their most advanced weapons, their most perfect hate. And when the Doctor dodged and tricked and cheated his way out of certain death a thousand times, they hated him all the more. Subtlety is not a Dalek trait, but they are capable of it. They developed a weapon that was also a trap – the Temporal Exterminator. An elegant weapon, really. The last thing it does is kill you.
When you’re hit by the Temporal Exterminator, it starts unravelling and eroding your time line in both directions – forwards and backwards. The first event that it unravels is the moment when you’re actually hit by the Exterminator, so you never remember being shot by it. The unravelling effect moves along your own timeline, corroding it. Events in your past stop making sense; your future becomes disconnected, disjointed. You might think you’re losing your mind, or just keep running and never notice that your past’s melting away. It’s only when the exterminator effect envelops your whole timeline that the weapon kills you, erasing you from history forever.
At some point in his timeline, the Doctor was hit by the Temporal Exterminator. He doesn’t remember it happening, because that’s the first event to be erased. But it’s killing him. He needs help.