Every Dark Thought (audio story)

Every Dark Thought was the first story in the Bernice Summerfield box set The Story So Far: Volume Two. This story marked the first time Benny encountered the Valeyard.

Publisher's summary
The Doctor has asked for Benny's help digging up some mysterious ruins. He claims they contain the secret of eternal life. Why would the Doctor want that?

Plot
Whilst Benny is working at possible religious site on Ogoychao, the Doctor shows up in his damaged TARDIS and asks for help in learning how to defeat the Caragot. They attack and Benny, the Doctor and Professor Liyi Chen head into the now-accessible cave to find the information they need, which Liyi, who initially blames the Doctor for bringing the Caragot here, says is convenient. Meanwhile, the Caragot integrate Marco, a member of Liyi's team.

As Liyi has a theory regarding the location of the central chamber, the Doctor has her lead the way through the caves, but they find that the caves are shifting and the layout is inconsistent. They come across a narrow bridge which the Doctor crosses first when Liyi questions him always putting her in front and soon encounter Chorus, who attempts to drive them away and whose life Benny saves before the bridge collapses. Chorus says that he is from Kensior Beta and came to Ogoychao centuries ago to be healed by the caves; they are in fact Riculi and excrete a liquid containing lifeforms which heal the sick and grant immortality.

The group reach the Riculi's nest and Liyi accesses a communication device which she uses to change the tunnel layout when they hear the Caragot approaching. Separated from Benny and Liyi, the Doctor forces Chorus to fetch a container that he might use to transport the liquid for his own use, holding him at gunpoint. The Caragot integrate Liyi for her knowledge and Benny falls when a tunnel opens beneath her feet. She finds the Doctor and witnesses him shooting Chorus, which he makes no attempt to deny. She accuses him of being an impostor, but he insists that he is the Doctor's future, born from the weight of their guilt and obligations.

The Doctor admits that he cannot regenerate, that he is afraid of death and that the Caragot are not conquerors but mindless genetic experiments who could become dangerous if they integrate his mind as they are planning to. They run, but the Caragot use the communication device to move the tunnels into a loop. Benny and the Doctor return to the central chamber whilst the Caragot are looking for them and the Doctor instructs the Riculi to create a formula which will ensure that any regeneration will not restore his typical compassionate characteristics.

When the Riculi corner them, Benny claims that she, the Doctor and Liyi have consumed a formula which will prove deadly to the Riculi should they integrate them. The Riculi release Liyi and begin the process of effectively turning themselves into gelignite, leading Benny, the Doctor and Liyi to run through the tunnels to escape before they explode. The Doctor is slowed down by his efforts to keep his cure from spilling, so Benny knocks it from his hands. He remains behind to collect what cure he can whilst Benny and Liyi escape. The Caragot explode and the Riculi are apparently killed, but Benny believes that the Doctor can survive anything in any form.

Cast

 * Bernice Summerfield - Lisa Bowerman
 * The Valeyard - Michael Jayston
 * Professor Liyi Chen - Liz Sutherland-Lim
 * Chorus - Mark Elstob
 * The Caragot - Ross Ford

Worldbuilding

 * The planet Ogoychao has a tourist resort on the mountain with expensive cocktails.
 * The Doctor has taken apart the whole console to find a fault, preventing the TARDIS from travelling correctly. He believes either the lateral stabilisers have fallen out of phase, or there's an imbalance in the helmic regulator; possibly both.
 * The Doctor is thousands of years old.
 * He explains that the Cloister Bell sounds throughout the TARDIS, but he doesn't know where it is.
 * The Doctor has tea and a fruitcake from Christmas, 1888.
 * The Caragot are parasitic gastropods with bonded cybernetic armour, a genetic experiment that ran rampant. There are no more than 100 of them. They integrate people that look "nutritious", making their intelligence part of their own and possibly killing them (the faces can be seen under their skin), but the victim can be de-integrated before digestion. They deploy a steam bomb that leaves structures intact.
 * The Doctor explains that the translation circuit is less reliable with written language.
 * Liyi hears everyone speak Mandarin.
 * After the Caragots attack, a member of the archaeological team begins to mention something "under the Centauri Convention.
 * Chorus is a non-human from Kensior Beta, whose people don't live centuries.
 * The "riculi" are the dominant lifeform on Ogoychao, living tunnels whose bodies are "here" but "not here," existing in another dimension and displacing rock when they pass through it. Their excretions treat ageing like a disease, and the Doctor theorises there may be micro-organisms in the liquids as he can hear them talking faintly. They can specify elixirs to order, as they analyse a person's body as they walk through the tunnels, learning how their biology works.
 * He "splintered" from the Doctor before his final incarnation, a causal imbalance, meaning he only has this life and cannot regenerate. As such, Benny doesn't consider him to be a true regeneration of the Doctor, saying that he's a twisted little fragment that "just fell off the back of a lorry."
 * The Valeyard plans to enslave the Caragot.
 * The Valeyard mentions the Web of Time, implying he still respects it.
 * Benny guesses that the TARDIS controls won't respond to the Valeyard because he's not a proper Time Lord.

Continuity

 * Benny has met the Doctor when he was younger, (AUDIO: Benny's Story) and when he was older. (PROSE: Big Bang Generation)
 * The Cloister Bell rings. (TV: Logopolis, et al.)
 * The Doctor has a knife from an 18th century Chinese assassin. (TV: The Talons of Weng-Chiang)
 * The Doctor implies to Benny that she's not the only archaeologist he's travelled with. (TV: Silence in the Library, COMIC: The Swords of Kali)
 * Benny mentions the Doctor doing his "big picture" stuff. (PROSE: Theatre of War, AUDIO: The Shadow of the Scourge)
 * The Valeyard mentions the Doctor trying to deny him his right to exist. (AUDIO: The Brink of Death)