# Doctor Who season 16

The sixteenth season of British science fiction television series Doctor Who, known collectively as The Key to Time, began on 2 September 1978 with The Ribos Operation and ended with The Armageddon Factor. The arc was originally conceived by producer Graham Williams, who had proposed it as part of his application for the producer's job in 1976. The name refers to a powerful artefact, the segments of which are what the Fourth Doctor and his companions, Romana and K9, search for during the season. Anthony Read continued in his role as script editor from the previous season. Douglas Adams also became script editor alongside Read.

## Synopsis

A figure calling himself the White Guardian commissions the Doctor and K9, assisted by a new companion, the Time Lady Romana, to find the six segments of the Key to Time, a cosmic artefact resembling a perfect cube that maintains the equilibrium of the universe. Since it is too powerful for any single being to possess, it has been split into six different segments and scattered across space and time, disguised by the raw elemental power within them into any shape or size. However, since the forces balancing the universe are so upset, the White Guardian needs to recover the segments of the Key to stop the universe so that he can restore the balance. The White Guardian also warns the Doctor of the Black Guardian, who also wishes to obtain the Key to Time for his own purposes. In the final episode, the Black Guardian, disguised as the White Guardian, attempts to take the Key from the Doctor. However, the Doctor sees through the figure's charade and orders the segments of the Key to Time to once again become scattered across all of time and space, bar the sixth, which he reinstates as Princess Astra. Afterward, the Doctor decides to install a device called a randomiser into the TARDIS' navigation system for a period of time to make his following voyages unpredictable to evade the Black Guardian.

### The six segments

In some stories, the segment in its disguised form is an integral part of the story, whereas in others, the segment is merely an incidental object.
* The first segment is disguised as a lump of Jethrik, a valuable rock mineral on the planet Ribos.
* The second is the planet Calufrax, shrunk to miniature size by the space-hopping pirate planet of Zanak.
* The third is the Great Seal of Diplos, a jewelled pendant which had been stolen by a criminal of that planet and brought to Earth.
* The fourth is part of a statue on the planet Tara.
* The fifth was an unspecified religious artifact that had been consumed by a squid on the swamp world of Delta Magna's third moon, causing it to turn into a gigantic monster named Kroll that the natives worship as a god.
* The final segment is a woman, the Princess Astra of the planet Atrios.

## Casting
### Main cast

* Tom Baker as the Fourth Doctor
* Mary Tamm as Romana
* John Leeson as Voice of K9
Tom Baker continued his role as The Fourth Doctor, and saw the introduction of Romana played by Mary Tamm. This season was the only one to feature Tamm as the first incarnation of Romana, as Tamm left the programme after only one season because she felt that the character had reverted to the traditional assistant role and could not be developed further. The second incarnation, played by Lalla Ward (who also appeared in this season as Princess Astra), began her run in the first serial of the next season (Destiny of the Daleks).

## Serials

Douglas Adams took over as script editor from Anthony Read for The Armageddon Factor. Season 16 consists of one long story arc encompassing six separate, linked stories.
| No. story | No. in season | Serial title | Episode titles | Directed by | Written by | Original release date | Prod. code | UK viewers (millions) | AI |
| 98 | 1 | The Ribos Operation | "Part One" | George Spenton-Foster | Robert Holmes | 2 September 1978 (1978-9-2) | 5A | 8.3 | 59 |
| 98 | 1 | The Ribos Operation | "Part Two" | George Spenton-Foster | Robert Holmes | 9 September 1978 (1978-9-9) | 5A | 8.1 | — |
| 98 | 1 | The Ribos Operation | "Part Three" | George Spenton-Foster | Robert Holmes | 16 September 1978 (1978-9-16) | 5A | 7.9 | — |
| 98 | 1 | The Ribos Operation | "Part Four" | George Spenton-Foster | Robert Holmes | 23 September 1978 (1978-9-23) | 5A | 8.2 | 67 |
| The Doctor is recruited by the White Guardian to seek the six segments of the Key to Time. The quest for the first segment takes them to Ribos, a medieval planet that galactic confidence trickster Garron is trying to sell to the Graff Vynda-K. ||||||||||
| 99 | 2 | The Pirate Planet | "Part One" | Pennant Roberts | Douglas Adams | 30 September 1978 (1978-9-30) | 5B | 9.1 | 61 |
| 99 | 2 | The Pirate Planet | "Part Two" | Pennant Roberts | Douglas Adams | 7 October 1978 (1978-10-7) | 5B | 7.4 | — |
| 99 | 2 | The Pirate Planet | "Part Three" | Pennant Roberts | Douglas Adams | 14 October 1978 (1978-10-14) | 5B | 8.2 | 64 |
| 99 | 2 | The Pirate Planet | "Part Four" | Pennant Roberts | Douglas Adams | 21 October 1978 (1978-10-21) | 5B | 8.4 | 64 |
| The quest for the second segment takes them to the planet Zanak, which has been hollowed out and fitted with hyperspace engines, allowing its insane cyborg Captain to materialise it around other smaller planets and plunder their resources. ||||||||||
| 100 | 3 | The Stones of Blood | "Part One" | Darrol Blake | David Fisher | 28 October 1978 (1978-10-28) | 5C | 8.6 | — |
| 100 | 3 | The Stones of Blood | "Part Two" | Darrol Blake | David Fisher | 4 November 1978 (1978-11-4) | 5C | 6.6 | — |
| 100 | 3 | The Stones of Blood | "Part Three" | Darrol Blake | David Fisher | 11 November 1978 (1978-11-11) | 5C | 9.3 | — |
| 100 | 3 | The Stones of Blood | "Part Four" | Darrol Blake | David Fisher | 18 November 1978 (1978-11-18) | 5C | 7.6 | 67 |
| The quest for the third segment takes them to Earth, where an ancient criminal who stole the segment disguises herself as the Celtic goddess Cailleach. ||||||||||
| 101 | 4 | The Androids of Tara | "Part One" | Michael Hayes | David Fisher | 25 November 1978 (1978-11-25) | 5D | 9.5 | — |
| 101 | 4 | The Androids of Tara | "Part Two" | Michael Hayes | David Fisher | 2 December 1978 (1978-12-2) | 5D | 10.1 | 65 |
| 101 | 4 | The Androids of Tara | "Part Three" | Michael Hayes | David Fisher | 9 December 1978 (1978-12-9) | 5D | 8.9 | — |
| 101 | 4 | The Androids of Tara | "Part Four" | Michael Hayes | David Fisher | 16 December 1978 (1978-12-16) | 5D | 9.0 | 66 |
| The quest for the fourth segment takes them to the planet Tara. The Fourth Doctor and Romana find themselves embroiled in the political games of the planet Tara, where doppelgangers, android or otherwise, complicate the coronation of Prince Reynart. ||||||||||
| 102 | 5 | The Power of Kroll | "Part One" | Norman Stewart | Robert Holmes | 23 December 1978 (1978-12-23) | 5E | 6.5 | — |
| 102 | 5 | The Power of Kroll | "Part Two" | Norman Stewart | Robert Holmes | 30 December 1978 (1978-12-30) | 5E | 12.4 | — |
| 102 | 5 | The Power of Kroll | "Part Three" | Norman Stewart | Robert Holmes | 6 January 1979 (1979-1-6) | 5E | 8.9 | — |
| 102 | 5 | The Power of Kroll | "Part Four" | Norman Stewart | Robert Holmes | 13 January 1979 (1979-1-13) | 5E | 9.9 | 63 |
| The quest for the fifth segment takes them to the third moon of Delta Magna, caught in the middle of a dispute between the crew of a methane refinery and the natives (known as 'Swampies'). ||||||||||
| 103 | 6 | The Armageddon Factor | "Part One" | Michael Hayes | Bob Baker and Dave Martin | 20 January 1979 (1979-1-20) | 5F | 7.5 | 65 |
| 103 | 6 | The Armageddon Factor | "Part Two" | Michael Hayes | Bob Baker and Dave Martin | 27 January 1979 (1979-1-27) | 5F | 8.8 | — |
| 103 | 6 | The Armageddon Factor | "Part Three" | Michael Hayes | Bob Baker and Dave Martin | 3 February 1979 (1979-2-3) | 5F | 7.8 | — |
| 103 | 6 | The Armageddon Factor | "Part Four" | Michael Hayes | Bob Baker and Dave Martin | 10 February 1979 (1979-2-10) | 5F | 8.6 | — |
| 103 | 6 | The Armageddon Factor | "Part Five" | Michael Hayes | Bob Baker and Dave Martin | 17 February 1979 (1979-2-17) | 5F | 8.6 | — |
| 103 | 6 | The Armageddon Factor | "Part Six" | Michael Hayes | Bob Baker and Dave Martin | 24 February 1979 (1979-2-24) | 5F | 9.6 | 66 |
| The quest for the sixth and final segment takes them to Atrios, a world at war with its planetary neighbour Zeos. But the Black Guardian is closing in. ||||||||||

## Broadcast

The Key to Time was broadcast from 2 September 1978 to 24 February 1979.

## Home media
### VHS releases

| Season | Story no. | Serial name | Number and duration of episodes | UK release date | Australia release date | USA/Canada release date |
| 16 | 98 | The Ribos Operation | 4 x 25 min | April 1995 | June 1995 | September 1996 |
| 16 | 99 | The Pirate Planet | 4 x 25 min | April 1995 | June 1995 | September 1996 |
| 16 | 100 | The Stones of Blood | 4 x 25 min | May 1995 | July 1995 | March 1996 |
| 16 | 101 | The Androids of Tara | 4 x 25 min | May 1995 | July 1995 | March 1996 |
| 16 | 102 | The Power of Kroll | 4 x 25 min | June 1995 | August 1995 | September 1996 |
| 16 | 103 | The Armageddon Factor | 6 x 25 min | June 1995 | August 1995 | September 1996 |

### DVD and Blu-ray releases

All releases are for DVD
| Season | Story no. | Serial name | Number and duration of episodes | R2 release date | R4 release date | R1 release date |
| 16 | 98–103 | The Key to Time | 26 × 25 min. | — | — | 1 October 2002 |
| 16 | 98–103 | The Key to Time: The Ribos Operation The Pirate Planet The Stones of Blood The Androids of Tara The Power of Kroll The Armageddon Factor | 26 × 25 min. | 24 September 2007 16 November 2009 | 7 November 2007 | 3 March 2009 |
* ↑ Stories available in Region 1 only, with minimal restoration and extras (individually or as a box set)
* ↑ Special edition. Known collectively as The Key to Time. Only available as a box set in Regions 2 and 4. Stories available individually or as a box set in Region 1. All serials contain four episodes each, apart from The Armageddon Factor, which has six episodes.
* ↑ Limited release
* ↑ Re-release

## In print

| Season | Story no. | Library no. | Novelisation title | Author | Hardcover release date | Paperback release date | Audiobook release date |
| 16 | 098 | 52 | Doctor Who and the Ribos Operation | Ian Marter | 13 December 1979 | 13 December 1979 | 3 March 2011 |
| 16 | 099 | — | The Pirate Planet (unabridged) | James Goss | 5 January 2017 | 1 February 2018 | 5 January 2017 |
| 16 | 099 | — | Doctor Who and the Pirate Planet (abridged) | James Goss | — | 11 March 2021 | — |
| 16 | 100 | 59 | Doctor Who and the Stones of Blood | Terrance Dicks | 20 March 1980 | 20 March 1980 | | — |
| 16 | 100 | — | The Stones of Blood | David Fisher | — | 14 July 2022 | 5 May 2011 |
| 16 | 101 | 3 | Doctor Who and the Androids of Tara | Terrance Dicks | 24 April 1980 | 24 April 1980 | — |
| 16 | 101 | — | The Androids of Tara | David Fisher | — | 14 July 2022 | 5 July 2012 |
| 16 | 102 | 49 | Doctor Who and the Power of Kroll | Terrance Dicks | 29 May 1980 | 29 May 1980 | 7 October 2021 |
| 16 | 103 | 5 | Doctor Who and the Armageddon Factor | Terrance Dicks | 26 June 1980 | 26 June 1980 | 6 June 2019 |
* ↑ Number in Target's Doctor Who Library, if applicable
* ↑ Published by Target's parent companies (Allen Wingate, W. H. Allen, BBC Books) unless otherwise indicated
* ↑ Published by Target Books (or by BBC Books under the Target Collection umbrella) unless otherwise indicated
* ↑ Unabridged from BBC Audio/AudioGo unless otherwise indicated
* ↑ Published by BBC Books