The one where Adric pretends to be an idiot.
The TARDIS arrives on the planet Deva Lokka, where the peaceful native Kinda are being screwed with by an imperialist human expedition. (They even wear pith helmets.) The expedition has been reduced to three people: Sanders, the bluff leader; Todd, the kind scientist who wishes she could get closer to the Kinda; and Hindle, the security guy, an already mentally unstable jobsworth who is being bullied into utter insanity by Sanders. The rest of the expedition seems to have gone missing entirely (which doesn't help Hindle's mental state).
Nyssa is suffering from a mysterious mental clouding (well, from not being added as a series regular until after the script was finished), and gets to stay in the TARDIS for the whole story. Tegan falls asleep under some magical wind chimes, and finds a tremendously sinister guy called Dukkha invading her Chiaroscuro dreamscape. He proceeds to Mind Rape her for two episodes until she finally agrees to let him possess her body.
Meanwhile, the Doctor and Adric encounter the expedition. Sanders leaves to explore, and Hindle promptly goes utterly batshit and has the Doctor and his new friend Todd imprisoned because he thinks the plants are plotting against him and the Doctor and Todd are in on it. Adric goes over to Hindle's side, although at least this time his decision to side with the villain is clearly because he's humouring Hindle and hopes that he can stop him from doing anything too horrific.
Sanders ventures out in a sort of human-sized mecha and encounters Panna, a Kinda shaman, and her apprentice Karuna. It turns out that the Kinda are matriarchal, and only the most powerful women can speak, the men and weaker women communicating by telepathy. They give Sanders the Box of Jhana, a Kinda artefact that they think will hopefully communicate the Kinda worldview to him and make him and the other humans leave. However, it regresses him emotionally to the age of about ten. He takes the box back to the base, where Hindle forces the Doctor to open it to see what it will do to him. It gives the Doctor and Todd a vision of Kinda culture, and luckily fails to drive them insane as well. Hindle also manage to enslave some Kinda by making them look into a mirror, tricking them into thinking he's captured their very souls in the reflective glass.
The now-possessed Tegan encounters a Kinda man, Aris, and transfers the possession (marked by a living snake tattoo) to him. He develops the ability to talk, and incites the confused Kinda to violently assault the human base. Meanwhile, Hindle and the childish Sanders have wired the place to explode rather than let themselves get taken. They then start playing like little boys with a model city.
The Doctor and Todd escape from the base and meet up with Panna and Karuna. Panna tells them that the evil snake force that has taken over Tegan is the Mara, an evil entity that feeds off destruction. It also turns out that the Mara will take over any non-telepathic entity that uses the wind chimes for visionary dreams, so it's all the Doctor's fault for letting Tegan sleep under them. She shows the Doctor and Todd a vison of the horrible things that will happen if the Mara isn't stopped, and then drops dead. Fortunately, thanks to Kinda telepathy, Karuna gets her memories and merges Panna's personality with her own.
The Doctor, Todd and Karuna find Tegan and wake her up. She thinks she just had a horrible nightmare, but they explain to her how badly things are messed up. They all reach the human base in time to see Aris and the Kinda attack it. Adric hold them off using the brain-controlled mecha, which promptly Mind Rapes him because he doesn't know how to use it properly. (Yes, there's a lot of that in this story.)
Todd manipulates Hindle into opening the Box of Jhana himself just as he is about to blow everyone up, and the experience shocks him back to sanity. The Doctor and Karuna then get the Kinda to help them trap Aris in a circle of mirrors (solar panels from the base) and the Mara leaves his body, materialises as a snake, and dies. Because evil can't take seeing itself reflected.
A now-sane Hindle and Sanders reconcile with one another and decide to be nicer people in future, and all the humans decide to declare the planet unsuitable for human colonisation so the Kinda will be left in peace. The Doctor declares that the Mara has been defeated, a bit prematurely. The Doctor and companions leave for further adventures.
- Absentee Actor: Nyssa only has cameos in episodes one and four, due to contractual issues related to her having been a guest character the previous season. One wonders why she couldn't have simply been assigned Todd's role in the story.
- Adventurer Outfit: Hindle and Sanders wear a variant.
- Arson, Murder, and Jaywalking: Hindle scolds Adric, saying he'll teach him "not to lie. Not to commit treason. And to wash behind the ears."
- Back from the Dead: Panna gets reborn in Karuna.
- Better to Die than Be Killed: Hindle eventually concludes that it's better to blow up the whole Dome, with all of them inside, than to allow to Kinda to kill them.
- Blind Seer: Panna.
- The Caligula: Once he's put in charge, Hindle goes off the deep end, throwing out barely-comprehensible rants and eventually concluding that the best way the end the threat of the trees is to destroy the entire base with all of them in it.
- Care-Bear Stare: The Box of Jhana is meant to have this effect, although it turns out that the effects on male humans can be more extreme and unpredictable.
- Characterisation Click Moment: Peter Davison's first two stories saw him largely out of action and largely undefined. This story sees him really find his footing, with his curious, eager, jovial, yet ultimately naive approach.
- Chewing the Scenery: Between the gloriously evil hamminess of The Mara, Hindle's batshit insane shouting, and Panna, it's a miracle any scenery was left to chew.
- Cool Old Lady: Panna.
- A Day in the Limelight: Each of The Doctor's companions was given a story where they could take a bigger role this season. This is Tegan's. She gets to get possessed!
- Demonic Possession: The Mara does this using, of all things, a set of wind chimes.
- Distaff Counterpart: Panna's short-temperedness and penchant for exposition brings to mind the First Doctor.
- Distressed Dude: The Doctor spends an entire episode being locked up in a cage.
- Doomsday Clock: Panna's vision of what will happen if the Mara gets loose has many, of different technological levels
- Earthy Barefoot Character: All the Kinda, even when Hindle forces some of them into partial human uniforms.
- Eldritch Abomination: The Mara, which starts out possessing people to escape into our world and then manifests as a huge snake.
- Everybody Lives: The only person who definitely dies in this story is Panna, and she partially survives thanks to her Mental Fusion with her apprentice.
- Fake Defector: Adric, with only partial success.
- Garden of Eden: A balmy forest free of predators, forbidden (within the base) fruit, a corrupting influence taking the form of a serpent...yeah, just a few allusions.
- George Lucas Altered Version: The DVD release features an optional frighteningly realistic CGI upgrade for the Mara, from a dorky-looking inflatable rubber prop.
- Hot Scientist: Todd.
- Innocent Aliens: The Kinda.
- Insane Equals Violent: Hindle.
- Insane Troll Logic: Hindle's reasoning for blowing the base to bits; if the base is destroyed, it can't be put in danger.
- Manchild: Sanders for a while after he opens the box, although it's suggested to be the effect of shock.
- Mental Fusion: Panna and Karuna, after Panna's bodily death.
- Me's a Crowd: In Tegan's nightmare, she is surrounded by illusory clones of herself, until she begins to doubt her own identity enough for the Mara to dominate her.
- Mind Rape: Tegan's encounter with the Mara has been compared to a rape scene. Remember that Doctor Who is a family programme.
- Mini-Mecha: The Total Survival Suit. Standing still, one can imagine it to be an impressive, boxy, 80's-style power armor, folded up into storage mode. Then it starts moving...
- Noble Savage: Subverted a bit: it's implied that the Kinda used to be a hi-tech race, but manipulated their biome to the point that they could give up technology and live a blissful hunter-gatherer idyll with no fear of predators, famine or disease.
- Nobody Calls Me "Chicken"!: How Todd manipulates Hindle into opening the Box at the climax.
- One-Word Title
- Only Sane Man: Adric. For most of the latter half, he's the only person inside the base who is not going insane or believes their soul to be trapped inside a mirror.
- Pinball Protagonist: The Doctor spends almost half the story in a jail cell, and subsequently is mostly just there to explain what's going on to Todd while the Kinda solve their own problems. Tegan spends most of the story possessed and Nyssa is completely missing in action. The most proactive character from Team TARDIS is Adric; sure, everything he tries fails, but at least he's doing something.
- Psychopathic Manchild: Hindle eventually ends up like this when Sanders leaves him in charge. The effect is chilling.
- Red Right Hand: People possessed by the Mara, or dream manifestations of it, get a snake tattoo on their arms and red-stained teeth.
- Sanity Slippage: Hindle's slipping when the story begins; by the end of the first episode, he's really starting to lose it.
- Scaled Up: The unfortunate final form of the Mara.
- Shout-Out: The Word for World Is Forest by Ursula K. Le Guin is a definite influence.
- Shout-Out to Shakespeare: The Doctor quotes The Tempest in the cave:Such stuff as dreams are made of.
- The Siege: Hindle thinks the trees are going to attempt a siege of the Dome; later on, the Kinda actually do.
- Single-Biome Planet: Justified; the planet was terraformed by the Kinda's ancestors so they could live anywhere without shelter or agriculture.
- Supporting Protagonist: The writer, Christopher Bailey, later acknowledged that the Doctor doesn't actually do very much in this story.
- Take That!: Sanders is named after the central character of Sanders Of The River, a now-notorious series of stories by Edgar Wallace glorifying the British Empire as wise, benevolent rulers of childlike Africans.
- Tools of Sapience: The Kinda necklaces, which characters note look remarkably like DNA double-helices.
- Ultimate Evil: The Mara qualifies for this.
- Walking Shirtless Scene: All the male Kinda wear only sarongs and go bare-chested.
- What Does This Button Do?: Adric's first reaction to the Total Survival Suit it to close the hatch, which activates it. The Doctor patiently explains to him that there is a difference between scientific enquiry and meddling.
- What Happened to the Mouse?: It's never explained exactly what happened to the three missing human explorers, although it's implied that Panna tried to use the Box of Jhana on them and they either went completely insane, or went completely native and joined the Kinda.
- Women Are Wiser: The Kinda certainly think so; only women are supposed to have the power of speech, and Panna thinks only a woman or an "idiot" male could look into the Box of Jhana without going mad.
- Wrong Genre Savvy: In a different kind of Doctor Who story, Hindle's belief that the plants were plotting against him might have been entirely correct.