The Dalek Protocol (audio story)

 was the first story, a prequel of sorts, in the Dalek Universe series produced by Big Finish Productions. It was written by Nicholas Briggs and featured Tom Baker as the Fourth Doctor, Louise Jameson as Leela, John Leeson as K9, Jane Slavin as Anya Kingdom and Joe Sims as Mark Seven.

Publisher's summary
The Earth mission to Exxilon is nearing completion after many long years. Enough parrinium has been mined to stop the spread of the deadly space plague. But suddenly, the power-draining beacon from the Exxilon city is inexplicably reactivated, stranding the humans.

The Doctor, Leela and K9 are stuck too, right on top of the remains of the city – under attack!

Somewhere nearby, the android agent Mark Seven is enacting his secret orders while the Doctor’s estranged future companion, Anya Kingdom, is hoping for redemption.

And heading inexorably towards them all… the Daleks!

Part one
to be added

Part two
to be added

Part three
to be added

Part four
to be added

Cast

 * The Doctor - Tom Baker
 * Leela - Louise Jameson
 * K9 - John Leeson
 * Anya Kingdom - Jane Slavin
 * Mark Seven - Joe Sims
 * Gislen - Jez Fielder
 * Ellasi Craig - Anna Mitcham
 * Bernard / Bellal / The Daleks - Nicholas Briggs

Crew

 * Cover Art - Ryan Aplin
 * Writer & Director - Nicholas Briggs
 * Executive Producer - Jason Haigh-Ellery and Nicholas Briggs
 * Music and Sound Design - Jamie Robertson
 * Producer - David Richardson
 * Script Editor - John Dorney
 * Daleks, the Kingdom Family, Mark Seven and Bellal created by Terry Nation
 * K9 created by Bob Baker and Dave Martin

Worldbuilding

 * The Doctor is very much aware of Mark Seven and also refers to him as a hero of the Dalek Wars. He is also aware of him being an android with a positronic brain.
 * Reading Mark Seven's memories, the Doctor discovers that the Daleks are also dying from the Space Plague. This explains their presence on Exxilon and why they wish to mine all of the parrinium.
 * When Mark Seven's undercover identity was discovered, the Daleks distilled within him the Dalek Protocol, turning him into a Dalek agent.

Continuity

 * Anya recalls the Doctor telling her about Leela being a "savage", leading her to be aware of her being a previous companion. This allows her to reach the conclusion about this Doctor having yet to meet her. (TV: The Face of Evil, et al.)
 * The Doctor and Leela recall their previous encounter with the Exxilons on E9874. (AUDIO: The Exxilons)
 * The Doctor reunites with Bellal, and frequently discusses his previous visit to Exxilon. (TV: Death to the Daleks)
 * Mark Seven and Anya Kingdom would later go on further missions. (AUDIO: Queen of the Mechonoids)
 * Anya mentions the Anti-Dalek Force and the Doctor refers to Mark Seven as a hero of the Dalek Wars. (PROSE: Terror Task Force et al.)
 * K9's weaponry proves effective against the Daleks. (COMIC: Doctor Who and the Dogs of Doom)