The Fifth Doctor takes Peri and Erimem to Tibet, for an Edwardian cricket match with some brave British explorers. While Peri and Erimem mock him extensively for just how English he can be, the cricket match is interrupted by a giant black cloud, which first hypnotises Erimem and subsequently drags her far away. A voice, an old and equally English gentleman, taunts her and makes her doubt everything she holds dear. Her friendship with Peri and the Doctor, her happy childhood, and whether or not she's even welcome in the TARDIS. It also makes her think she's dead, showing her her own funeral and the Doctor's heartfelt eulogy. By imitating the voices of Peri, the Doctor and Amenhotep II, the creature tries to convince Erimem that she's seen as worthless by everyone, that she's got nothing left, and that her only option now — in limbo — is to either trust him or suffer eternal hell. He reveals that Amenhotep II, before his death, planned to had Erimem thrown to the lepers rather than to suffer his daughter to become Pharaoh.
While Erimem is being thoroughly broken, the Doctor and Peri organise a search party for her, together with the expedition's leader (who's a pompous ass on the outside and a sweet, insecure man deep down) and the journalist (who just wants to get home to his wife and kids and write some proper news). The mysterious voice does a passing imitation of the Doctor and tries to convince Peri to give up the search before it's even started, but is quickly caught when the actual Doctor walks in, miffed at being impersonated.
As it turns out, the "roof of the world" is not only more than it seems, but has actually been hollowed out as a perfect ice tomb for an ancient Eldritch Abomination. Amenhotep II, who had a fondness for astronomy and ancient lore, had stumbled on the creature during his research and decided to have it permanently entombed in the mirrored ice of Tibet, to force it into solitude with its own reflection forever. But young Erimem mistook the creature's papyrus scrolls for toys, accidentally read the ancient chants when she was a child, and became extremely vulnerable to the creature's influence because of it. The creature plans to use her as a herald to bring itself back into the world — which her father realised, and which is why he planned to had her thrown to the lepers. Peri and the explorers save the day by pouring liquid nitrogen on the thing and bombing the cave's entrance.
Adrian Rigelsford was to have written The Dark Dimension, the briefly-proposed thirtieth anniversary film in 1993. He was also the only Doctor Who writer to have a story released while serving prison time.
- Abusive Parents: Erimem learns that her father, Amenhotep II, didn't quite view her the way she thought he did. But it was all to protect her.
- A Form You Are Comfortable With: The old ones take the form of humans when needed.
- Batman Gambit: The Doctor has people indicate as if they're going upstairs whilst hiding in the basement so that their chasers go upstairs.
- Call-Back: The Doctor mentions Jellybabies.
- Chekhov's Gun: The Doctor is rather miffed at Peri and Erimem when they use liquid nitrogen on the TARDIS swimming pool to turn it into an ice skating rank. Peri eventually uses the stuff to kill the Beast.
- Chekhov's Skill: Peri's skill at making plaster casts comes in handy.
- Climbing the Cliffs of Insanity
- Compelling Voice: The old ones.
- Confronting Your Imposter: Davey's impersonation of the Doctor is going well till the real Doctor walks in.
- Dreaming of Times Gone By: Erimem of her times in Egypt.
- Emotion Eater / Evil Alien Creatures Need Fear Badly
- Glowing Eyes of Doom: Erimem gains these once she's posessed.
- Hearing Voices: Erimem from the start of the story. At first it seems like she's losing her mind, but this being Doctor Who it's an alien superpower trying to take over her mind.
- Horde of Alien Locusts: the Doctor theorises that this is what the Old Ones truly are.
- "I Know You're in There Somewhere" Fight: The Doctor and Peri try to talk Erimem out of her possession.
- Intrepid Reporter: One of these is part of the General's entourage.
- Miles Gloriosus: General Alexander Bruce.
- Mix-and-Match Critters: The beings crossbred with other species, causing various kinds, in a desperate attempt to live longer.
- Newsreel: Parodied.
- Quintessential British Gentleman: The Fifth and his LOVE for Cricket!
- Reality Is Unrealistic: General Alexander Bruce believes Sherlock Holmes is real. And says Watson couldn't've made him up.
- Sealed Evil in a Can: The Old ones are buried in the Roof of the world.
- Smug Snake: Lord Davey (or, rather, the creature possessing him)
- Spot the Imposter: The Doctor calls this one of The Oldest Ones in the Book. Subverted Trope seeing as the imposter drops the disguise straight after the Doctor enters the room.
- Sufficiently Advanced Alien: The beings are the inspiration for the four horsemen of the apocalypse, the boogeyman et al.
- Survival Mantra: Erimem maintains her sanity by reciting Lewis Carroll's "You Are Old, Father William" from Alice in Wonderland — a poem she adores because it reminds her so much of the Doctor. Also a Continuity Nod, since Erimem was reading Alice in Wonderland in the previous story, and the book became a key element of the "Zagreus" episode.
- Thanatos Gambit: Erimem's death.
- That's No Raincloud
- They Fight Crime!: The Doctor and the General.
- Tom Boy And Girly Girl: Erimem compared to Peri. When dealing with a potential Panty Shot Peri protests and complains and before she knows it Erimem has already climbed out of the top hatch.