Following on from The Dalek Contract. The Daleks and Cuthbert are trying to open the Quantum Gateway, the Daleks planning to use it to conquer all reality. However the Gateway could destroy the Universe. The Doctor destroys the Daleks by attuning the Gateway to their DNA.
Sadly this was the last story to feature Mary Tamm, who died of cancer a few months after the recording finished. She was undergoing treatment while the series was being recorded, but didn't complain and wanted to make the series.
Tropes:
- And the Adventure Continues: It ends with Romana declining to return to Gallifrey and instead continue adventuring with the Doctor.
- Compound-Interest Time Travel Gambit: The Doctor claims Cuthbert may have done this to start his Conglomerate business empire.
- Complexity Addiction: The Doctor practically depends on the Daleks inevitably overreaching themselves with a convoluted plan to take over the entire universe, because the bigger their plans get, the more likely he can spot a flaw in them.
- Cosmic Keystone: The Quantum Gateway. The Doctor even compares it to a God.
- Defrosting Ice Queen: Romana has been slowly defrosting throughout all her adventures with the Doctor, and she thaws completely at the end when the Doctor offers to take her back to Gallifrey and she declines.
- Disney Death: The Doctor appears to be blown up along with the spaceship he was travelling on. Naturally, the TARDIS was hidden aboard and he escaped in the nick of time.
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Harsher in Hindsight: The final line of the story is Romana telling the Doctor that she won't be letting him out of her sight for some time yet. As Mary Tamm died not long after recording this set of stories, these would be the last words we ever hear this incarnation of Romana say. - It's All About Me: Though Cuthbert makes a token effort to stop the Daleks needlessly executing people and says he doesn't want reality to be torn apart, he refuses to actually stop his Gateway project outright so that he can ensure the dominance of the Conglomerate in the past.
- Kill It with Fire: K9 unloads rocket fuel onto some Daleks, enabling them to be killed this way.
- Multiversal Conqueror: What the Daleks plan to become by opening the Gateway.
- Outgrown Such Silly Superstitions: A Dalek claims there are no Gods, to which the Doctor says the gateway is like one.
- Temporal Paradox: At the end it is claimed Cuthbert may be a living one. He went into the Quantum Gateway, apparently going back in time to build his company.
- They Really Do Love Each Other: Romana realizes she does indeed care for the Doctor and enjoys his company only when she thinks he's been killed.
- Timey-Wimey Ball: Cuthbert used the Quantum Gateway to travel into the past and plant the seeds for his empire. The Doctor notes how bizarre it is that he could do this but still exist in the future.
- Too Dumb to Live: Cuthbert continues to believe that the Daleks are his obedient servants long after everyone else knows better.
- Voice Changeling: The Doctor is able to use his thoughts to talk in a Dalek voice.
