In the settlement of Purity Bay, being clean, sterilized and careful is the most important rule— for good reason, because the mysterious Takers steal away anyone who is sick or injured, never to be seen again.
The Doctor, Tegan, Turlough and Nyssa are greeted with suspicion upon their arrival and immediately find themselves swept up in a political battle between the fanatical Sister Mertil and her younger, more progressive stepdaughter Seksa. Meanwhile, the whispering, ghost-like Shades lurk in the forest, determined to make themselves heard...
The Whispering Forest contains examples of:
- Ambition Is Evil: Sister Mertil is extremely power-hungry, marrying Purity's leader almost immediately after his first wife's accidental death and attempting to take over his role immediately after he disappears. Also, it turns out the first wife's death wasn't an accident after all.
- Autodoc: The Takers are actually medical robots from a crashed hospital ship.
- Call-Back: The Doctor says he had the TARDIS scan the universe for mentions of Richter's syndrome.
- Call-Forward: The green crescent moon is the universal sign for healthcare.
- Captain Obvious:Turlough: It's a forest!
Tegan: Thanks for pointing that out, Turlough.
- Cargo Cult: The people fear the Takers, who turn out to be robots.
- Crush. Kill. Destroy!: The possessed Takers.
- Death Seeker: The Shades.
- Evil Redhead: Turlough is mistaken for a Taker because of his red hair— "Redthatch" is another name the citizens of Purity use for the Takers.
- Fainting: One of the soldiers, Hervey, who's already not that sturdy on his feet, lays eyes on the Doctor and Nyssa, and immediately faints.
- Foreshadowing: Tegan complains of headaches and expresses a reluctance to sleep throughout the play, which foreshadows The Reveal at the end.
- Ghost in the Machine: The Shades take hold of the Takers towards the end.
- Gilded Cage:Tegan: The prettiest prison I've ever seen.
- God Guise: Turlough pulls this on the people from Purity. They believe him to be a Taker, so he puts on a booming voice and tells them to leave Nyssa alone when they gang up on her.
- Hoist by His Own Petard: Jestan and Mertil both die because of their arrogance.
- Just Between You and Me: Mertil actually pulls this.
- Knight Templar: Mertil is worse than the rest of her people, and will do anything for what she thinks is just. She's just not that just.
- Nice Job Breaking It, Hero!: The people of Purity only manage to get into the Takers' ward because Turlough and Nyssa leave a (deceased) Taker's husk outside of the forcefield.
- Our Ghosts Are Different: The Shades, the incorporeal beings who haunt the forests surrounding Purity are the remaining echoes of the people infected with Richter's Syndrome who were unsuccessfully euthanized by the medibots.
- Out, Damned Spot!: Not because of guilt of a murder, but the people on Cherdor scrub themselves so clean their skin is red and grated.
- Plot Lock: The Deadlock seals from the New Series make an appearance.
- The Fundamentalist: Mertil, whose obsession with hygiene and being "pure" goes beyond even the society's ingrained germphobia.
- Madness Mantra: "Take flesh. Make fresh."
- Mauve Shirt: Poor Hervey.
- Reports of My Death Were Greatly Exaggerated: Anulf and his wife.
- Shout-Out to Shakespeare: The Doctor says there is "Something rotten in the state of Chobel".
- Super OCD: The entire society of Purity is based on this— the inhabitants constantly scrub themselves with harsh chemicals to the point that their faces and hands are permanently raw and red, and hair is forbidden as it gets dirty too easily.
- Villain Teleportation: The Takers.
- Wicked Stepmother: Mertil.
- Tegan: What did they mean? My condisssion?
The Doctor: I'm not sure. Come on into the TARDIS, we can run some tests.
Tegan: Tessstsss? What are you going to do? Hypnotissse me? Will you ssstop me dreaming? Will you check my armsss to sssee if the mark isss ssstill there?
Nyssa: Tegan we don't know if this is what that is!
Tegan: We know exacsssactly what thisss is.
The Doctor: Nyssa help me into the TARDIS.
Tegan: Time to go? Too green for you here? You told me I was rid of it. Its coils still inside! I live, Doctor! THE MARA LIVES! Hahahhaha!