6 March 1984
Christopher Gable (Sharaz Jek), John Normington (Morgus), Robert Glenister (Salateen), Maurice Roëves (Stotz), Martin Cochrane (Chellak), Roy Holder (Krelper), Barbara Kinghorn (Timmin), David Neal (President), Ian Staples (Soldier), Matthew Waterhouse (Adric), Sarah Sutton (Nyssa), Janet Fielding (Tegan), Mark Strickson (Turlough), Anthony Ainley (The Master), Gerald Flood (Voice of Kamelion), Colin Baker (The Doctor) 
|Written by||Robert Holmes|
|Directed by||Graeme Harper|
|Produced by||John Nathan Turner|
Arriving on the barren world of Androzani, the Doctor and Peri find themselves embroiled in a long-running underground war. Military troops mount an armed blockade whilst gunrunners bring in weapons for the sinister, masked renegade, Sharaz Jek. Meanwhile, lethal androids guard the caves, a deadly creature lurks in the shadows, killing all in its path. At the heart of the conflict is a substance called Spectrox — the most valuable item in the universe… and the deadliest!
The very presence of the Doctor and Peri on Androzani sets in motion a chain of events that will have dramatic consequences for everyone involved. As the situation gets even more desperate, the Doctor realises time is running out – both for Peri and himself. Will the Doctor make the ultimate sacrifice to save his young friends life..?
- This story had the working title of Chain Reaction.
- Peri mentions a reticular vector gauge.
- Nicola Bryant, or her stunt double, bounces after slipping down the cliff-face in episode one, obviously having landed on a safety cushion of some kind.
- Morgus is (or was, before being deposed by Timmin) “the richest man in the Five Planets”, chairman of the Sirius Conglomerate and a descendant of the first colonists.
- The Doctor claims to be able to store oxygen for several minutes.
- The Doctor confesses to Peri he tried to keep a diary, but he never finds the time to update it.
- Despite the title, the Doctor notes that The caves are in fact blowholes.
- The maps of the caves shown on screen bear an uncanny resemblance to the video game Dig Dug.
- In the alternate universe spawned by the Valeyard (The Trial of a Time Lord – Parts 13 to 14), the Fifth Doctor finally succumbed to the Valeyard‘s influence at this point, taking the bats milk himself and letting Peri die. Thus, the Fifth Doctor becomes a wraith of the Valeyard, until his restoration At The hands of the Seventh Doctor in Matrix.
- In Timewyrm: Revelation, it is revealed that after the Fifth Doctor died, his personality was manifested as the Doctor’s conscience, but buried by the Seventh Doctor after his regeneration, until Ace freed him in the aformentioned book.
- Following this, the Sixth Doctor goes through a brief period where he subconsciously blames Peri for his previous self’s death, and tries to distance himself from her while telling himself he’s working towards a greater good, until he finally realizes this in Burning Heart.
- Oddly enough, the new Doctor looks exactly like Commander Maxil from the Gallifreyian Security Guard, who stunned the Fifth Doctor and later held him prisoner until his execution in Arc of Infinity.
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