On Solos the Marshal is once again hunting down a local mutant native. When two accompanying guards catch up to the Marshall they find him standing over the body of the native, but are ordered to report a local native has been found dead - the cause unknown.
In his laboratory on Earth, whilst working on a minimum inertia superdrive for Bessie, a strange dark sphere materialises on a desk. It's a message pod from the Time Lords, and the Doctor has been given the task of delivering it. The Doctor enters the TARDIS, followed quickly by Jo, before it de-materialises on a pre-programmed course. The TARDIS materialises on board a space station - Skybase One - orbiting the planet Solos in the 30th century empire - inside a small storage area. The Doctor hands the message pod to Jo, and using the sonic screwdriver opens the door to get into the Skybase. A computer alerts personnel to a malfunction in the storage area door.
Elsewhere on Skybase One Ky arrives from Solos to attend a conference to demand that the 'Overlords' stop murdering his people. Varan is also attending the conference, and his people have been responsible for killing the mutants. Whilst Ky and the other Solonians go off to de-contamination Varan is told the Marshal wants to speak to him privately.
The Doctor and Jo, wandering around the Skybase, don't see anyone. Using the sonic screwdriver the Doctor breaks into storage area 3 moments before they are attacked by a mutant who had been part of Varan's bodyguard. When the computer alerts a malfunction in the storage area 3 door guards go to investigate and kill the mutant and arrest the Doctor and Jo.
The Marshal is discussing the conference with the Administrator and is told that Earth can no longer afford the planet, and so they are giving the Solonians independence. The Marshal protests, and says the atmosphere could be cleaned up, and the mutant natives - Mutts - could be destroyed. The Marshal isn't keen on returning to Earth - things could be difficult for ex-colonial officials.
The Administrator and the Marshal go to see the Doctor and Jo, and the Doctor claims that 'Overlord Centre' sent them, but they are suspicious, and the Marshal wants to know how they got there without a pass and there have been no shuttle arrivals. Jo hands the message pod to the Administrator and the Marshal, but nothing happens. They demand that the Doctor opens the pod, but the Doctor tells them it will only open for the correct recipient.
The Administrator and the Marshal leave for the conference, but the Doctor, Jo and a guard, Stubbs, are able to watch the telecast in the reception area. As Jo distracts Stubbs the Doctor gives him a nerve pinch and escape. The Administrator, depsite protests from Ky, makes a speech about what the Earth Empire has done for Solos, and what it has given them. As Ky protests more the Marshal orders him to be arrested. In the chaos the Administrator is hit by a dart fired by Varan's son, which has been given to Varan by the Marshal.
As guards are called in Ky escapes from the conference room. He passes the Doctor and touches the pod, which opens are he runs past. Jo goes after Ky, and he uses as a shield as he transports himself and Jo back down to Solos. In a transfer station on Solos Ky tells Jo she has to stay behind as the surface is polluted, and Overlords cannot survive on the surface without masks. When alarms sound and a guard starts shooting Ky takes Jo onto the surface.
In the Skybase the Doctor is given the bad news by the Marshal. The Marshal tells the Doctor that during the daylight no human can survive on Solos without an oxymask. It is caused by a nitrogen isotope and that ultra-violet rays from the sub cause a poisonous mist. Jo has very little time, and the Marshal agrees to intensify the search if the Doctor tries to open the message pod.
The Doctor is given a laboratory on the Skybase to try to open the box. The Doctor was hoping for more advanced equipment, and notes that the existing equipment seems geared more towards atmosphere manipulation. The Doctor notices a circuit that is about to overload, and when he turns if off a scientist, Jaeger storms in. Jaeger is ordered to help the Doctor open the pod.
On the surface, pursued by guards, Jo collapses, struggling to breathe, and is carried by Ky. When the guards split up Ky attacks one of them and gives his oxymask to Jo. He takes her to a disused mine and helps her to start breathing properly. Inside the mine Jo no longer needs the mask, and tells Ky the pod was meant for him. Whilst they hide in the cave Ky tells Jo about how his people have become slaves to the Overlords, and that the planet has become polluted and is causing mutations.
In the Marshal's office Varan's son has been caught. The Marshal thanks Varan's son for killing the Administrator, then kills him. When Varan enters the room he is fired upon by the Marshal, but escapes. The Marshal orders guards to capture Varan.
In the laboratory the Doctor asks Jaeger why humans came to Solos, and is told it is because the planet is one of the richest sources of Thaesium. As they talk the Doctor completes his particle reversal machine, which should be able to turn the pod inside out. It works briefly before the machine overloads. The Marshal and Stubbs enter the laboratory looking for Varan. When the Doctor hears the Marshal say Varan is turning into a mutant he asks the Marshal if he can go on the 'Mutt-hunt' with them.
The Doctor and Stubbs find Varan in a herbology section. Stubbs is ready to kill Varan, but the Doctor notices he has no signs of mutation and Varan tells them the Marshal killed his son, and tells them about how the Marshal had the Administrator killed. If Solos has independence then the Marshal would be out of a job. But now martial law is in place the Marshal is in charge.
Returning to the laboratory the Marshal tells the Doctor that Jaeger could use some help on a different project. Jaager plans to bombard the planet with rockets to filter the ultra-violet light and make the planet breathable. This could kill the Solonians, and the Doctor will not help in the genocide. Another guard, Cotton, send Jaeger to the Marshal and tells the Doctor about Jo still being on the surface. The Doctor comes up with a plan which would allow his to transport down to Solos. Using the equipment in the laboratory the Doctor is able to overload the Skybase's power supply. The Doctor, with Varan, are able to transport to Solos using the transfer station's power.
On the surface the Doctor gets Ky to take him to Ky and Jo. Unlike humans the Doctor is unaffected by the pollution. As they leave the planet is affected by firestorms. In the mine Ky tells Jo there were no firestorms until the Marshal began his experiments to make the air breathable for humans. Jo is startled when she sees a full mutant in the cave. Usually the mutants are harmless, but this one is more aggressive. Ky frightens it off using a torch, and he and Jo move further back in the mine where they find more mutants. Varan leads the Doctor to the case but is reluctant, at first, to go inside. They arrive in time to rescue Ky from the mutants, but Jo, trying to avoid the mutants, runs further into the mine and finds herself in a strange cavern filled with lights. Before the collapses she sees the silhouette of a figure coming towards her.
After the mutants have gone the Doctor hands Ky the message pod, and it opens when he holds it. Inside are stone tablets with strange signs and text written in the language of the old ones. Ky tells the Doctor that signs similar to those are present all over Solos. Ky tells the Doctor that there may be one person who understands the language - Sondergaard.
The Marshal calls Stubbs and Cotton to his office, and tells them to go to the surface of Solos and kill Varan, Ky and the Doctor. He gives them grenades developed by Jaeger.
Jaeger has been monitoring the firestorms, and has noticed that whilst the planet gets hotter there is no decrease. Solos' temperature is rising, perhaps to a temperature that humans cannot live in. He surmises that during the 500 years they have been there Solos has been in spring, and now it is moving into summer. There is also an increase in the mutation rate.
In the mine tunnels, whilst searching for Jo, Ky gets an instinctive feeling that some areas feel safer than others. They continue their search and find Jo. Stubbs and Cotton are sent by the Marshal to find Ky and the Doctor, and when he hears that they have found them he orders the grenades to be fired which start spreading gas into the mines. Unaware of the gas Jo tells the Doctor and Ky about the silver figure she saw, and moments later a silver suited figure appears, beckoning to them.
The figure leads the group to a lead covered room. The figure introduces himself as Sondergaard. Sondergaard explains that he noticed that Solos was becoming a slave colony, and that the Marshal intercepted his call to Earth, and that he had hidden in the caves in a shelter away from the radiation, and kept up with his research. Sondergaard says that things are changing on Solos. At first it was natural, but Jaeger's experiments had sped things up. The Doctor is concerned about Solos, but also curious why he was sent to Solos, and what the tablets mean.
Sondergaard is amazed by the tablet, and says he has seen the same hieroglyphs in the old temples. Sondergaard attempts to translate the tablets, and realises the tablets show the beginning of civilisation on Solos. As bombardments threaten the entire mountain Ky leads Stubbs, Cotton and Jo to a Varan's village whilst the Doctor stays behind with Sondergaard.
Examining the tablets the Doctor realises that each of the four represents a season, and that each season is 500 years long. The Doctor also realises why the Time Lords sent him to Solos. The Doctor asks Sondergaard to show him the centre of the Thaesium mine. Even in a radiation suit Sondergaard is unable to go far and collapses, leaving the Doctor, who is able to stand the radiation, to go on alone. Further on the Doctor finds what appears to be a glowing statue, and removes a green crystal before returning to pick up Sondergaard and return to the shelter. The Doctor tells Sondergaard that the mutation is supposed to happen, that it's part of the life-cycle of the planet that happens every 500 years, and that the mutants are just an intermediate form. The Doctor wants to examine the crystal in further detail, especially as it is not in anyway radioactive. The only facilities to analyse it are in Jaeger's laboratory in the Skybase.
When Ky, Jo, Stubbs and Cotton make it to Varan's village they are captured. With the Overlord weapons, and Ky and Jo as human shields, Varan plans revenge against the Marshal. Stubbs and Cotton are able to get Varan and the villagers into the transfer station and on board the Skybase. In the Skybase the Marshal receives news of the imminent arrival of an Earth Council investigator. The Marshal tells Jaeger that he wants the Mutts eliminated and the atmosphere on Solos breathable by the time the investigator arrives. As the countdown starts to launch the rockets a message comes through about unauthorised people in the transfer section. In the Skybase fighting breaks out betweeb Varan's men and the Marshal and his guards. The Marshal fires at Varan fracturing the hull and sending Varan into space as the rockets fire toward Solos.
After the Skybase is stabilised the Marshal quickly arranges a firing squad for Ky, Jo, Stubbs and Cotton, but it is interrupted by Jaager who tells the Marshal that the attack was a failure and that every rocket malfunctioned. He explains that instead exploding in the atmosphere all the rockets hit the surface, contaminating it meaning no-one will ever be able to set foot on Solos.
On the surface the Doctor and Sondergaard are caught in the rocket attack. During a lull in the attack they find the village destroyed, and make for the transfer station. The Doctor notices the contamination from the ionisation crystals in the rockets has already begun to take effect. Learning the Doctor is still alive the Marshal organises his guards to capture the Doctor. The Doctor makes it to the transfer station before the guards and transports up to the Skybase.
The Doctor finds Jo, Ky, Stubbs and Cotton, and is caught by the Marshal. The Marshal orders the Doctor to help Jaeger fix the problems that have been caused using particle reversal - using Jo as leverage.
Left alone with just one guard Jo is able to free herself and take the guard by surprise, and free Ky, Stubbs and Cotton. Once freed Cotton and Jo contact the investigator and give a brief summary of events. When Stubbs is killed by the Marshal Jo, Ky and Cotton make their way back to the teleport. The Doctor needed a part from the transport, meaning it does not work the Jo tries to use it, and they are re-captured by the Marshal.
On the surface Sondergaard comes across a group of mutants and talks to them. He tries to explain that they are not sick. The mutation is supposed to happen naturally, but the experiments have caused the mutation to go wrong, and that hopefully the Doctor can put it right.
In the laboratory the Doctor and Jaeger complete the machine and are able to reverse damage done by the rockets. The Marshal orders them to continue and make the atmosphere breathable for humans. The Doctor refuses, and the Marshal threatens Jo before the Investigator announces his arrival. Jo is taken back to a refuelling lock where Ky and Cotton are being held. Cotton realises that when the Investigator's ship, the Hyperion, docks it will begin to refuel, and the thaesium running through the lock will kill them. Their only chance is to get inside the fuel probe when it enters the tunnel and escape back into the Skybase.
The Marshal and the Doctor meet the Investigator in the Marshal's office. They go through the Marshal's report, and the Marshal tried to justify his actions. When asked if agrees with the Marshal's report the Doctor reluctantly agrees, fearing for Jo. With no contrary evidence the Investigator clears the Marshal of blame. Jo, Ky and Cotton turn up just in time to act as witnesses, and the Doctor tells the Investigator the truth about the Marshal and how he kept Jo as hostage to ensure his co-operation.
When the Investigator asks about Sondergaard the Doctor says he is on the surface, but Sondergaard is brought into the office. He has transported to the Skybase - along with one of the mutants. Upon seeing the mutant the Marshal quickly grabs a weapon and destroys it, and the Investigator orders the Marshal's guards be set free.
The Doctor, Jo and Sondergaard escape to the laboratory where the Doctor analyses the crystal. The Marshal, once again in charge, orders the Doctor to complete the atmosphere change, and takes Jo, Ky, Sondergaard and Cotton as hostages and places them in the radiation chamber. Sondergaard hands the crystal to Ky, and he begins to change. As he changes into a mutant he draws away all the radiation, and then completes the change into a spirit. After the Ky spirit disappears the door opens freeing Jo, Sondergaard and Cotton.
In the laboratory the Ky spirit appears and kills the Marshall, and thanks the Doctor before disappearing. With the Marshal gone Sondergaard returns to Solos to help the mutations use the crystal to complete their mutations properly, and Cotton is given command of the Skybase pending its return to Earth.
Regular castJo Grant: Katy Manning;
Guest castMarshal: Paul Whitsun-Jones; Ky: Garrick Hagon; Cotton: Rick James; Stubbs: Christopher Coll (1-5); Varan: James Mellor (1-4); Varan's Son: Jonathan Sherwood (1-2); Administrator: Geoffrey Palmer (1); Jaeger: George Pravda (2-6); Sondergaard: John Hollis (3-6); Old Man: Sidney Johnson (3); Solos Guards: Roy Pearce (4), Damon Saunders (5); Guard Warrior: David Arlen (4); Mutt: John Scott Martin (5); Investigator: Peter Howell (6);
Uncredited cast: Old Man: David J. Graham; Guard Warrior: Ian Elliott; Earth Control Guards: (all 6) Gary Dean, Barry Hooper, Keith Urry, Mick Urry; Advisors: Ken Nazarin, Evan Ross; Mutts: Laurie Goode, Bill Gosling, Nick Thompson Hill, Mike Mungarvan, Rick Newby, Eddie Sommer, Mike Torres; Skybase Guards: Keith Ashley, Ali Baba, Dave Carter, Ronald Gough, Atley Harvey, Dennis Plenty, Ron Tingley, Terry Walsh, David Waterman; Solonians: Reg Cranfield, Brychan Powell, Vic Taylor, Peter Whitaker; Guard Leaders: Damon Sanders, Martin Taylor; Warriors: Derek Chafer, Alex Hood, Steven Ismay, Terry Sartain, Terry Walsh;
|BBC 1||318||Episode One||Sat 8 April 1972||5:50 pm - 6:15 pm||9.1M||29th|
|BBC 1||319||Episode Two||Sat 15 April 1972||5:50 pm - 6:15 pm||7.8M||38th|
|BBC 1||320||Episode Three||Sat 22 April 1972||5:50 pm - 6:15 pm||7.9M||36th|
|BBC 1||321||Episode Four||Sat 29 April 1972||5:50 pm - 6:15 pm||7.5M||44th|
|BBC 1||322||Episode Five||Sat 6 May 1972||5:50 pm - 6:15 pm||7.9M||44th|
|BBC 1||323||Episode Six||Sat 13 May 1972||5:50 pm - 6:15 pm||6.5M||67th|
Chislehurst Caves, Kent; Finsbury Caves, Stonehouse Farm, Kent;
Television Centre Studio not known;
Bloopers and mistakes
Episode 1: The Doctor tells Jo that he couldn't open the package if he wanted to twice in the same speech!
Notes and trivia
Episodes One and Two are only held as film prints and NTSC recordings.
This programme has no other working titles, or they have not been yet been entered.