The Eighth Doctor runs into a flotilla of Type 70 TARDISes in the Vortex, and steers around them, thinking it must be the Flag Day of Rassilon or something. (Yes, of course he's wrong, but that's not important right now.)
So instead of paying attention to the plot, the Doctor and Charley travel to the remote Cimmerian System to unravel the mystery of its disappeared sun. Darkness has embraced the scientific base on Cimmeria IV, leaving its three resident scientists blind and hopelessly lost. When Charley and the Doctor find them, they discovered that the scientists' eyes have been literally burned away. And one of them has gone insane from the experience.
The culprit is a tiny, innocent-looking little thing: a Cimmerian, whose body has adapted to the lack of sun by having evolved a sensory system based around taste. When the creature realises that its victims are now missing something called "eyes", it makes a Heroic Sacrifice to restore them.
The Doctor, however, doesn't know that, and has decided to finish what the scientists came for in the first place: a giant web of artificial suns. And that's when he finds out that the light of the suns will attract a species called "Solarians", who were long ago the reason the Cimmerians turned off the sun in the first place.
In a panic of guilt and self-loathing, the Doctor put Charley in the care of the scientists and goes off to save the day (and possibly make a Heroic Sacrifice or two, if he gets a chance to). Charley won't have it and follows him, with a good helping of What the Hell, Hero? Eventually, they figure out that the Solarians once lived on the planet with their sickness, and were healed compulsively by the Cimmerians at the cost of the Cimmerians' own lives. As a group of innate healers, they were unable to turn away the sick, and instead took the only other option: they turned off their sun and hid. Now, centuries later, they've evolved rapidly to live in perfect darkness.
The Solarians eventually arrive — and the Doctor expects a full-scale invasion fleet, and immediately starts monologuing at them. This rather confuses the Solarians, seeing as they're actually just a friendly team of archaeologists investigating their old planet. The Solarians and Cimmerians were of the same race all along.
- Bizarre Alien Biology: Inverted. The Cimmerians don't know what eyes are.
- Breather Episode: Although the episode has plenty of horror, it's one of the very few stories in a long line that don't involve a giant Timey-Wimey Ball.
- Broken Record: When ROSM has been exposed to too much Cimmerian radiation, he starts repeating small sentences.
- Calvin Ball: The Draft game.
- Dark Is Not Evil: Almost literally in this case. The Cimmerians plunged their planet into darkness in order to save themselves from the Solarians. A nicer race of aliens you couldn't encounter.
- Driven to Madness: The scientists are slowly growing more bitter and fearful the longer the story goes on.
- Everybody Lives
- Eyeless Face
- Eye Scream
- Foreshadowing: The Doctor quoting Shakespeare.The Doctor: "Jocund day stands tiptoe."
- ROSM detecting unidentifiable data from scanning Charley.
- Genocide Dilemma
- Good All Along: The Solarians were really archaeologists.
- Happy Ending
- Healing Hands: The Cimmerians. Unfortunely doing this too much kills them.
- Heroic Sacrifice: One of the aliens.
- Hidden Depths: A darker variant. Orllensa seems rational at first and then admits to having killed a mole of her previous team with a spanner. This unsettles Charley quite a bit.
- Hive Mind: The ROSM.
- Ignored Epiphany: A flotilla of TARDISes probably isn't important.
- Innocent Aliens: The Cimmerians.
- Insistent Terminology: Lifeform Doctor, Lifeform Charley.
- Is It Something You Eat?: ..Your eyessssss? What are eyessssss?
- Jerkass: Orllensa. She starts out snarky and rapidly becomes bitchy, unsympathetic and eminently unlikable - going so far as to use her injury (which another team member also has) as an excuse to simply be NASTY to everyone with no prompting.
- Lawful Stupid: ROSM in spades. The worst example is when he refuses to authorize use of the ship's weapons, because the Doctor and Orllensa were threatening to destroy company property.
- Light Is Not Good: The suns are considered dangerous to the Cimmerians.
- Double Subversion when they aren't.
- Logic Bomb: Similar. The Doctor can override the ROSM's programming by feeding it information to which it can make a logic conclusion.
- The Mole: One of the previous science teams had an spy amongst their ranks, who sabotaged the works as they finished.
- Name's the Same: The Doctor claims there are many races called the Solarians. Shows the Solarians here are unrelated to the Solarians from the Third Doctor text-story Prisoners of the Sun.
- Not So Different
- Obliviously Evil: The Cimmerians go around burning people's eyes out for like half the serial. They aren't trying to hurt anyone.
- Obstructive Bureaucrat: The Doctor considers the Time Lords these.
- No Antagonist
- Poor Communication Kills
- The Power of the Sun: The scientists are trying to set up a web of artificial suns.
- Robot Names:"I am the Rescue Operational Security Module T723 Rover Assault Unit 1."
- Shout-Out: The robots are called ROSM. The play "Rossum's Universal Robots" introduced the word "robot".
- Sssssnake Talk: The Cimmerians and Solarians.
- Those Two Guys: Mike and Haliard.
- Title Drop
- Trigger Happy: The Doctor pleads Orllensa to ask questions first, then shoot.