The Kro'ka places the Eighth Doctor, Charley and C'rizz in a jungle for his latest experiment. They're soon captured by a group of military rebels who have been keeping busy with an improvised Apocalypse Now re-enactment. The rebels are holed up in a giant cave, seemingly brainwashed by their Dark Messiah, Major Koth.
As the heroes stumble about and fail to get anything done whatsoever, something deep inside the cave starts probing at the Doctor's mind and decides it can use the Doctor for its purposes. It's also, however, telepathically causing Charley and C'rizz to become extremely crabby, and they lose their will (and soon enough, ability) to leave the cave at all. The entire rebel population has been trapped for years, without realising they're being held captive. They survive off the slimy nutritious soil that grows on the cave's surfaces.
The Doctor takes an inordinate amount of time to figure out that the cave is a giant sentient venus flytrap, and that it went berserk in all the wrong ways when it accidentally absorbed Koth. This turned it into somewhat of an Eldritch Abomination. The cave's next plan is to absorb the Doctor, which — after some teasing involving the TARDIS — it does. The Doctor uses this to his advantage, because being part of the cave allows him to control it if he concentrates. Unfortunately, this will eventually kill him, and he doesn't like to think about what would happen if he'd regenerate while part of a giant slimy cave monster. Fortunately, the local scientist makes a Heroic Sacrifice instead of the Doctor, and kills the monster by overloading its mind with The Power of Love.
The Kro'ka once again mocks the Doctor, and lets slip that he does understand the word "time". The Doctor has had enough of the Kro'ka's games, and realises that he was right all along: the planet is a laboratory, and everyone they've met in the past couple of months has been a test subject. He has no choice, however, but to keep playing, and the heroes head off into the next experiment. The Doctor also reveals what he hoped to find by diving into the Divergent universe: Rassilon.
- And I Must Scream: Implied to have happened to Koth.
- Arc Words: For the Divergent arc: death and rebirth, becoming food for other lifeforms, fluid consciousness between multiple beings, breaking free of the cycle, the next life and the beyond.
- Body Horror
- Brainwashed and Crazy: Sergeant Bryn.
- Later Charley.
- Character Development: Ever since Scherzo, the Doctor has been growing harsher and colder. This is mentioned by Charley In-Universe. And this is before being ruthlessly broken later in his life.
- Continuity Nod: Charlotte's memories are full of plum pudding.
- Dark Messiah: Koth."Despite all evidence of the contrary, you still believe in people's inherent goodness. Is that not the greatest lie of all?"
- Divided We Fall
- Does Not Like Guns: The Doctor.
- Eldritch Abomination: The Cave Creature.
- Failed a Spot Check / Too Dumb to Live: Giant moist cave with electric walls. Rivers of blood, gore and shit. Carcasses everywhere. Corrosive fluids that can eat through flesh. And still, nobody notices what's going on. Maybe that's because something's actively messing with their heads.
- Genius Loci: The cave.
- Heartbeat Soundtrack: Played With. It's an actual giant heart.
- Heroic Sacrifice: Ianto decides that he's expendable than the Doctor and takes his place in the Fusion Dance.
- Hollywood Acid
- Idiot Ball: As noted In-Universe, it is very difficult to believe that anyone would go far enough into such an obviously hostile environment to be ensnared by it, resistance movement or no.
- I'm a Doctor, Not a Placeholder
- I'm a Humanitarian: The Cave Creature.
- La Résistance: Koth organized his army to rebel against what he saw as injustices on Ondrockan. In reality, any intent he originally had died when he merged with the Cave Creature. Now all the rebels are is food for it.
- Mauve Shirt: Bryn.
- Meat Puppet
- More Than Mind Control: The Resistance Members and later The Doctor, Charley and C'rizz.
- Not So Different
- Not That Kind of Doctor: Ianto.
- People Farms
- The Plague
- The Power of Love
- Public Execution
- Running Gag: Someone remarks that the Doctor's mind looks smaller from the outside.
- The Swarm
- That's No Moon!
- Too Spicy for Yog-Sothoth: First Major Koth, whose emotions drive the Cave Creature insane. Then Janto, whose emotions kill it.
- The Undead
- Wham Line: When The Doctor and The Kro'Ka are discussing what the The Doctor is really looking for in the Divergent Universe.
- The Kro'Ka: What do you expect to find?The Doctor: Rassilon!