The Fifth Doctor and Nyssa accidentally end up on Earth... during the beginning of the Dalek invasion. Yes, that Dalek invasion. The 22nd century isn't doing very well, and as soon as the Doctor realises when they are, he scrambles back in the direction of the TARDIS as fast as he can. Nyssa gets stung by a wasp in the process, and her wound soon begins to get nasty.
The Daleks have other plans for him, though, and they use a time corridor to drag the Doctor over to the distant future, where only a few humans survive on Earth and the Daleks have some serious troubles of their own. A group of Daleks have started mutating into flying insectoid creatures, breaking free of their casings and destroying everything in their paths. Including Skaro. The Dalek Emperor forces the Doctor to go back in time and prevent the mutant infection from happening in the first place. A Thal scientist is reluctantly helping the Daleks, because even Daleks aren't as bad as the mutant things roaming around.
Nyssa, using her skill points in Science Hero, deduces that the Daleks use a collective gene sampling pool for their breeding stations and that wasp eggs, buried underneath a battered Dalek's skin, have caused the mutation. Several severe time paradoxes later, and with Skaro set to be destroyed in the future, the Doctor finds himself back on 22nd century Earth and facing a group of Daleks who have never even heard of him (or time travel) yet. It turns out that the Dalek Emperor avoided being destroyed along with Skaro by copying his consciousness into a Thal years ago — the best friend of the Thal scientist.
The Dalek Emperor desperately tries to explain to the 22nd century Daleks that the Doctor is their mortal enemy, that exterminating him won't help because a younger him will still defeat them all in the future, and that time travel is in fact possible. The Daleks (rather hilariously) don't believe a single word the Emperor says, but get suspicious enough to check the stung Dalek for wasp eggs, thus preventing the whole adventure from ever happening. The Thal scientist doesn't trust that solution and additionally charges forward with his antidote, and the Emperor smashes it to pieces, causing the web of time to short-circuit. When the Daleks from the mutant phase's timeline tried to capture the Doctor, they penetrated a weak point of the Vortex with their corridor, releasing a burst of temporal energy which generated a causal nexus. The centre of the paradox was the Emperor himself, who nearly created the mutant phase by going back in time to destroy it.
In the normal course of things, the 22nd-century Daleks would have detected and extracted the wasp DNA from the infected Dalek themselves; if the Emperor had convinced them to use the GK-50 pesticide instead, it would have failed to kill off the infection (since it was in an early stage and not responsive to the pesticide yet), which would thus have spread through the Dalek gene pool and created the mutant phase. Since the Emperor smashed the injection probe instead, this never happened; the mutant phase never existed, the Thals never worked for the Daleks and the Emperor never travelled back in time. Skaro was never destroyed, and the Doctor is entirely unable to explain to Nyssa what happened.
Part three of four in the Dalek Empire arc. An abridged one-hour cut of this story, originally included as a Feelie with issue 124 of Doctor Who Adventures, is legally available for free on Soundcloud
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Tropes:
- Absolute Xenophobe: Daleks contaminated by the Mutant phase get immediately exterminated. Wholly justified, in this case.
- Anachronic Order: For the Doctor and the Daleks it's very unclear where in their timelines they are, relative to each other; for the future Daleks it takes place after their encounters with the Fifth Doctor's future selves in the Dalek Empire arc, but for the Daleks on Earth they haven't even encountered the First Doctor yet.
- Biological Mashup: The Mutant Phase is a cross between a species of mutated wasps and Daleks.
- Body Horror: The Mutant Phase turns the entire Dalek (metallic shell included, somehow) into an insect like giant alien locust that eats everything.
- Body Snatcher: Ganatus gets taken over by the Dalek Emperor, or by a copy of his mind.
- Cassandra Truth: The Dalek Emperor trying to convince the Daleks of the past of the Timey-Wimey Ball at play.
- Dying As Your Self: The Dalek Emperor plans to do this with an Skaro Shattering Kaboom
- Enemy Mine: The threat of the Mutant Phase is so great that the Daleks and the Thals have been working together to capture the Doctor to get his help in finding a cure.
- Foregone Conclusion: The Doctor can't help the humans fight off the Dalek invasion because he has already will have done it several years in the future back in his First incarnation.
- Foreshadowing: Unlike the other episodes of the "Dalek Empire" arc, this one isn't a leadup to the specific events of the spinoff Dalek Empire, but rather the introduction of a plot element that will become important later - the fact that the Dalek Emperor can download his consciousness into a human (or Human Alien) brain.
- For Want Of A Nail: A Dalek getting stung by a wasp puts the Universe in danger.
- Genetic Engineering Is the New Nuke: The plants were genetically modified to attract wasps that kill harmful caterpillars. The wasps got a bit too enthusiastic and soon started killing humans. One of them got into a broken Dalek casing and laid its eggs underneath the Dalek's skin... nearly destroying the entire universe.
- Hand Wave: Why the Doctor is on this adventure yet would not save Adric; it doesn't get much of an explanation beyond "Temporal Paradox"
- "I Know You Are in There Somewhere" Fight: The Doctor pleads one last time with the Ganatus / Dalek Emperor.
- Insectoid Aliens: The Mutant Phase turns the Daleks into hundred-foot-long wasp-Dalek hybrid things that suck all the life force out of every planet they come across.
- Lesser of Two Evils: The Mutant Phase is such a threat to reality that the Daleks end up being this.
- Mind Screw: The resolution of the Temporal Paradox at the end is so complicated that Nyssa can't wrap her head around it.Nyssa: "Doctor, that doesn't make sense!"The Doctor: "How shall I put it. Paradoxes very rarely do; that's why they're paradoxes."
- Never the Selves Shall Meet: The Doctor and Nyssa arrive a few moments after they did the first time creating a Stable Time Loop on them getting lost earlier.
- Not That Kind of Doctor: The Doctor again
- Oh, Crap!: When the Doctor realizes when and where he is.
- One-Steve Limit: Averted - a Thal named Ganatus previously appeared in the TV series, suggesting it's a common Thal name.
- Rail Roading: The Daleks' Time Corridor is set up specifically to stop the Doctor from just running off somewhen else and ignoring the plot.
- That's No Moon: It's not a spaceship. It's a swarm.
- The Beautiful Elite: Played With when the blond and handsome Fifth Doctor gets briefly mistaken for a Thal.
- The Farmer and the Viper: Referenced by the Doctor as the Scorpion and the Frog
- The Plague: In two forms, one; the Mutant Phase, two; Ptolem has a virus that will kill all pre-Mutant Phase Daleks.
- The Nth Doctor: Alluded to by the Doctor. "Looks like we both have had a facelift since the last time we met!"
- Time-Travel Tense Trouble: The Dalek Emperor; see Cassandra Truth
- Timey-Wimey Ball: A merry chase through time to prevent something that never would have happened in the first place if the Emperor hadn't tried so hard to prevent it.
