Story 103 - The Armageddon Factor

In which the Doctor, Romana and K9 reach the end of their quest to locate the six segments that make up the Key to Time. The final piece lies somewhere on the planet Atrios. This world has been at war with its twin, Zeos, for many years. The TARDIS makes an emergency landing on Atrios after it is targeted by an Atrion missile. The locator wand seems to guide them to a sealed up section of the underground city - the surface being too irradiated for anyone to survive there. K9 burns a hole in the door, and they discover that there is a young woman trapped beyond. She is actually the Princess Astra, nominal ruler of Atrios. The military commander of the planet - the Marshal - has had her locked in this irradiated section in order to kill her. He is acting under some external influence.
Astra and her lover - medic Merak - want to contact Zeos in order to stop the war.
At first, the Doctor and Romana are taken to be Zeon spies. However, the Marshal suddenly changes his mind and asks the Doctor for help in defeating their enemy. The Doctor learns that the planet has only a handful of warships left. Before the Doctor and Merak can rescue Astra, she is abducted by tall black clad figures who emerge from a hidden transmat booth.
Romana discovers that behind a mirror in the War Room, which the Marshal frequently contemplates, there lies a hidden chamber. Within is a crystal skull, which acts as a communications device. The Marshal has a small black receiver hidden behind his ear. Romana then discovers that the TARDIS appears to have disappeared.

The Doctor is seized by the black clad figures and finds himself transported to Zeos. The creatures are the mutant servants of the Shadow. This wraith-like figure is working for the Black Guardian. He has taken the TARDIS. He wants the five segments which the Doctor has already obtained, and claims to know where the sixth piece is. The Doctor is able to stop the Shadow entering the TARDIS. He and his mutants vanish, content to bide their time. Back on Atrios, Astra's discarded coronet is picked up by the locator wand. She must have had contact with the segment. Assuming that the wand will lead him to the Princess, Merak steals it and uses the transmat to follow her to Zeos. Romana and K9 follow. The Doctor has discovered that Zeos is totally devoid of life. K9 meets a super-computer called Mentalis. This has been coordinating the defence of the planet as well as the attacks on Atrios. It is the Shadow who is influencing the Marshal. He instructs him to launch an attack on Zeos in his personal battle-cruiser - promising success. Mentalis will not defend itself - and its destruction will trigger a cataclysm that will destroy this entire region of space. The Doctor uses a time-sensitive material - chronodyne - to create a temporary sixth segment in order to partially operate the Key - and is able to lock the Marshal's ship into a time-loop. Unfortunately, this loop will stretch to breaking point within hours.

The Shadow sends a mentally-controlled Astra to try to steal the Key. The Doctor deduces that the Shadow must have a hidden base nearby. There is an artificial satellite in orbit between the warring planets. The Doctor pilots the TARDIS there. Romana is captured and even K9 falls under the mental control of the Shadow. The Doctor meets a fellow Time Lord - someone he was at school with. This is Drax. He was commissioned to build Mentalis for the Shadow, but then found himself held captive. The Doctor and Drax escape when they use the TARDIS dimension stabiliser to shrink themselves to an inch tall. K9 will act as a Trojan Horse, to carry them into the Shadow's control centre. It transpires that Princess Astra is the sixth child of the sixth house of the sixth dynasty of Atrios - and is in fact the sixth segment. To Merak's horror, she is transformed into the crystal segment when she touches the locator wand. The Doctor and Drax emerge from K9, grow to normal size, and are able to snatch the Key away from the Shadow. The Marshal's attack takes place, but the TARDIS forcefield causes his missiles to be deflected instead to destroy the Shadow's lair. The Black Guardian deserts his servant and he is destroyed. Drax informs the Doctor that he will be entering into business with the Marshal. The White Guardian appears on the TARDIS scanner. He congratulates the Doctor and Romana on successfully completing their mission, and requests that the Key be handed over to him. When he seems to shrug off Astra's extinction, the Doctor suspects all is not as it seems. It is really the Black Guardian. The Doctor orders the Key to disperse itself through Space and Time once more. Merak is therefore reunited with the Princess.

This six part adventure was written by Bob Baker & Dave Martin - their final collaboration on the programme - and was broadcast between 20th January and 24th February, 1979. This is the last story to be script edited by Anthony Read. His successor - Douglas Adams - was involved in an uncredited capacity. This is also the final story for Romana actress Mary Tamm. John Leeson steps down as the voice of K9 - though he will be tempted back for Season 18 - and beyond.
It marks the end of Season 16 - the linked Key to Time season.
A disappointing end at that. Producer Graham Williams and Anthony Read stated later that the problem with a linked season was that it tied you to a certain production order.
As it is, the quest for the Key segments has been very much confined to the background up until this story. The five earlier stories really needed to have more of an overt threat from the Black Guardian - such as their respective villains being more obviously his agents. Only Cessair of Diplos might be one.
The biggest disappointment is the conclusion, where the Doctor simply re-scatters the segments after going to all that effort to collect them. It is not clear what the brief operation of the Key has actually achieved.

Setting the Key aspects aside, it is not a bad story in its own right. Two planets at war, but with a couple of twists. One of the planets is actually now lifeless, the war being waged by a computer. Another twist is that there is a third party hiding in the shadows, stirring things up.
For a six parter things do not drag too much. This is partly due to the action being split between the three planets - episodes one and two on Atrios, three and four on Zeos, and five and six on the "Planet of Evil" - the Shadow's domain. Dialogue makes this out to be a planet, and it has rocky interiors, but the model makes it look like a space station.
Talking of models, there is some good work on show. Wisely, the battle sequences are depicted purely through the radar plots on the screen in the War Room.
The Marshal is played by John Woodvine. A very fine actor, he dominates the opening episodes but is then sidelined in a time loop for the second half. The Shadow is William Squire. The whole realisation of this villain is very good - from the vocal performance to the costume, with its skull-like face. The wet Merak is Ian Saynor, and the camp as a row of tents Shapps (the Marshal's second-in-command) is Davyd Harries. Drax is played as a Sarf London wide-boy by the late Barry Jackson. (He is supposed to have picked up the accent in a well known South London penal institution).
Someone who will figure large in the future of the series (and in the life of its then star) plays Princess Astra - Lalla Ward. Initially, another rather damp performance when she is playing the worthy royal. Once she starts getting tortured and mind-controlled, Ward has something to get her acting chops into.
Episode endings are:

1. The Doctor and Romana rush back to the TARDIS - only to discover that it has vanished...
2. In the transmat booth, the Doctor overhears Romana state that he has walked into a trap. Sure enough, there are two mutants behind him. They all vanish...
3. In his command ship. the Marshall launches his attack against Zeos - not realising that this will trigger Armageddon for this region of space...
4. As the TARDIS approaches his domain, the Shadow revels in the fact that the Key to Time will shortly be his...
5. The Doctor had intended that Drax shrink the mutant guard, but instead he turns the dimension stabiliser on them both - shrinking them and leaving the TARDIS door ajar...
6. The Doctor intends to keep out of the Black Guardian's way for a bit by fitting a randomiser unit to the TARDIS guidance systems.

Overall, the story must be judged on its job of finishing off the six story Key arc. In this, I think, it fails. As a stand alone story, with the Key aspects removed, it isn't all that bad.
Things you might like to know:

• Mary Tamm decided to leave because the role was not turning out the way it had been sold to her. She expected to be more of an equal with the Doctor, but felt that Romana was slipping into companion cliché behaviour. She subsequently stated that she would have come back for a regeneration scene had she been asked.
• Lalla Ward is descended from George Plantagenet - the Duke of Clarence drowned in a butt of malmsey by his brother Richard III. She was born Sarah Ward, daughter of the 7th Viscount Bangor. "Lalla" came from her attempts as a small child to say her own name.
• This may have been the last work by the Bristol Boys - Baker and Martin - but Bob Baker would go on to have one further story produced in his own right - Nightmare of Eden - in the following season.
• An early story suggestion was that the sixth segment was going to be the Shadow's shadow.
• It is suggested that the disguised Key segments all go back to the same places and times that the Doctor found them - hence Astra being returned to existence. There seems to be an obvious flaw in this if the locations are now all known. Perhaps Astra was an exception permitted by the Key - being a living being - and that new hiding places were found for the segments.
• Drax refers to the Doctor as "Theta Sigma" - which some people at the time took to be his real name. As was later confirmed in The Happiness Patrol, it is only a school nickname. 
• Thanks to the cancellation of Shada, this is the last ever six part story.
• Graham Williams was ill during the early stages of production. Former director David Maloney stepped in to help with the preliminary work.