You know, for a man who abhors violence, I took great satisfaction in doing that.
— The Doctor surveys the smoking remains of a Dalek
The TARDIS lands in a forbidding jungle, but with the Doctor slipping into a coma, Jo sets out to see if she can find help. She comes across a party of Thals, and stays in hiding aboard their crashed spaceship while they go to help the Doctor. After they have treated him, they tell him that they have travelled to this planet, Spiridon, to destroy a group of Daleks who have come to try and uncover the secrets of invisibility discovered by the natives.
Another Thal ship arrives and crashes (the Thals are evidently not great pilots) and the survivors tell of a force of ten thousand Daleks somewhere on Spiridon. The Doctor and the Thals find the Daleks in suspended animation in a cavern below the planet's surface. Using explosives, they blow up a rock wall separating the cavern from one of the planet's ice volcanoes, and the Daleks are destroyed.
The Supreme Dalek and his guards arrive on the planet, only to be stranded as the Thals steal their spaceship and the Doctor and Jo leave in the TARDIS.
- Continuity Nod: Upon meeting the Thals, the Doctor mentions the events of The Daleks and The Evil of the Daleks.
- Fearless Fool: The Doctor urges this on a prisoner, not to think himself such a coward
- Glowing Eyes: The local beasts, about their campfire
- Kill It with Ice
- Made a Slave: The Spiridons.
- Off-the-Shelf FX: The "force of ten thousand Daleks" is really quite blatantly a whole bunch of Dalek toys.
- People of Hair Color: The Thals are all blond.
- Pragmatic Villainy: When the Daleks are preparing to release their bacterial bomb, they administer vaccine to all their forces, including their Spiridon slave workers. This is not so much out of compassion but rather that they still need a cheap labour force to do the heavy work for them.
- Rock Beats Laser: It helps to have gravity on its side.
- Slave Race: The Spiridons.
- Stupid Sacrifice: Not only does Merak's attempted Heroic Sacrifice do absolutely nothing to delay the Daleks, it very nearly screws over the Thals completely, since the Daleks find the location of the Thals' explosive charges on his body. Only Jo's quick thinking prevents disaster for the Thal expedition.
- Suicide Mission: What the Thals think they face. For most of them it's right.
- Synthetic Plague: The Daleks are planning to use one to wipe out the Spiridons.
- Technical Pacifist: see page quote.
- There's No Place Like Home: Jo wants to return to Earth.
- The X of Y
- Humorously, "Planet" and "Daleks" are the most common X and Y. Really, this is the archetypical Doctor Who title!
- Trapped in Containment: The Daleks in the bacterial lab.
- Trojan Prisoner: Used by the Doctor, Jo, the Thals and some Spidron rebels to infilrate the caves.
- Truth in Television: Ice volcanoes, which sound like an oxymoron, actually exist, and were first discovered on Neptune's moon Triton.
- Wham Line: Somewhere on this planet are ten thousand Daleks!
- Worth Living For: One Thal is afraid after he finds this in Jo.
- You Can't Go Home Again: The Daleks in the bacterial lab, again, since they are immune to the virus.
- Note that the project leader was trapped in the lab, but an identical project leader is later in another room being exterminated by the Dalek Supreme. Either he suddenly gained magical escaping powers, or this second Dalek was the victim of a poorly-timed promotion.