The Apocalypse Element (audio story)

 was the first audio to feature Lalla Ward reprising her role of Romana II. It is also the first Sixth Doctor audio drama to feature the Daleks.

Publisher's summary
When the planet Archetryx is threatened by a Dalek assault squad, the Sixth Doctor and Evelyn become embroiled in an ever-deepening mystery. What has become of President Romana, missing for twenty years? What lurks in the vast gravity wells of Archetryx? What is the secret of the ancient element the Daleks are synthesising -- and how does Gallifrey feature in their plans?

The Doctor finds that if his oldest enemies cannot conquer the universe they will watch it go up in flames...

Plot
to be added

Cast

 * The Doctor - Colin Baker
 * Dr. Evelyn Smythe - Maggie Stables
 * Romana II - Lalla Ward
 * Monitor Trinkett - Karen Henson
 * Assistant Monitor Ensac - James Campbell
 * Commander Vorna - Andrea Newland
 * Coordinator Vansell - Anthony Keetch
 * The Monan Host - Toby Longworth
 * The Lord President of Gallifrey - Michael Wade
 * The Daleks - Alistair Lock / Nicholas Briggs
 * Vrint / Captain Raldeth - Andrew Fettes

Daleks

 * The Dalek force is led by a Black Dalek.
 * Twenty years ago the Daleks removed Etra Prime from space-time, kidnapping a Monan and Time Lord delegation including Lady President Romanadvoratrelundar.
 * Evelyn is shot by a Dalek, paralysing her legs.

The Doctor

 * The Doctor's status as Lord President has been revoked.

Elements

 * Particles found on Etra Prime are what the Daleks call the 'Apocalypse Element', an entropic power present in crystals which can channel mental energy and behave contrary to the laws of physics.

Galaxies

 * The Daleks detonated a particle of the Apocalypse Element in the Seriphia Galaxy, destroying everything in it.
 * Gallifrey's galaxy is a neighbour of the Seriphean Galaxy. It is four times the size of the Milky Way galaxy and home to over six hundred billion stars.

Gallifreyan technology

 * The Rod of Rassilon and the Sash of Rassilon are needed to manipulate the Eye of Harmony.
 * Much of Gallifreyan technology relies on an iris scan.

Other realities

 * The Doctor mentions Romana having been in E-Space.

Planets

 * Archetryx is host to a 'Time Treaty' of 'twenty of the greatest powers in space-time'.
 * Etra Prime is the oldest planetoid in the known universe.

Psychology

 * At one point, Evelyn worries that Romana has Stockholm syndrome, but she initially believes it to be called Stockbridge Syndrome.

Species

 * The Monan Host haven't yet managed dimensional transcendence with their time technology.
 * Species attending (and part of the treaty include: the Time Lords, the Monan Host and the Virgoans.

Science

 * The Gravity wells on Archetryx are subterranean shafts where zero gravity able is able to be manipulated.

TARDISes

 * TARDISes on Gallifrey are kept in TARDIS cradles.

Time technology

 * Archetryx is protected by a temporal barrier, inside which everything is one minute in the future.
 * The Monan Host's time craft has powerful engines, more so than even the Time Lords' TARDISes.

Continuity

 * It was established in NA: Happy Endings that Romana was Lady President of the High Council of the Time Lords.
 * This story goes some way to explain why the Eye of Harmony in the TARDIS in DW: Doctor Who (1996) required a human eye in order to open.
 * Due to these events, Romana later established the Temporal Powers, an alliance with multiple time-active factions. (BFG: Insurgency)
 * The Matrix records this event as happening during the Rassilon Era year 6796.8. (BFA: Neverland)
 * Romana would later meet a version of the Sixth Doctor from an alternative timeline who referred to himself as "Lord Burner." (BFG: Disassembled)