Terror of the Vervoids ( TV story ) Terror of the Vervoids was the unbroadcast title given to episodes 9 to 12 of " The Trial of a Time Lord " , the season - long story that constituted season 23 of " Doctor Who " . It was the third serial in the " Trial of a Time Lord " arc . While the previous stories of the season delved into past adventures of the Sixth Doctor , this story examined the Doctor ' s pending future . Using that anachronistic style , it introduced Bonnie Langford as companion Melanie Bush , deviating from the formulaic structure where a stranger found themselves meeting the Doctor for the first time , and vice versa . Instead , her character was a future companion that the Doctor had yet to meet - something later repeated with the character River Song 22 years later . Synopsis . The Time Lords have brought the Doctor to trial , accusing him of gross interference in the affairs of other planets . If he is found guilty he must forfeit all his remaining regenerations . In the hope of proving his innocence , Melanie Bush , an as - of - yet unmet companion from later in his life , is summoned to the court . Hopefully through her help , the jurors will be reassured in letting the Doctor go free by seeing what good acts he stands to commit as opposed to destructive ones . In his defence the Doctor tells of an adventure set on board the Hyperion III space liner in his future . Answering a distress call , the Doctor and Mel arrive on the liner just as a series of grisly murders begins . Plot . Part nine . The Doctor returns to the courtroom after a recess , given to allow him time to mourn Peri ' s death , which was revealed in the previous block of evidence . The Doctor begins his defence , showing events from his future . The galactic liner " Hyperion III " is a ship taking a supply of rare metals from Mogar to Earth in the year 2986 AD . The Doctor states that many of the passengers and crew will not survive the journey to Earth , for " [ someone determined to ] protect a secret hidden on the space liner . . . will become a murderer . " " On the spaceliner " Hyperon III " , an elderly man named Kimber thinks he recognises a fellow passenger as an investigator called Hallett . However , the passenger denies this , claiming that he is a mineralogist called Grenville . A trio of scientist passengers — Professor Sarah Lasky and her colleagues Bruchner and Doland — are alarmed that Grenville might be an investigator . Edwardes , the communications officer , detects a craft close to the ship — the TARDIS — but is unable to get a reply . Suddenly , an unseen figure attacks him and injects him with a syringe . He then uses the communication equipment to send a message to the TARDIS . On board , the Doctor and Mel pick up a Mayday message , stating " . . . perative traitor be identified before landing Earth . " They materialise within the " Hyperion III " s cargo hold , next to the hydroponics centre . The Doctor tells Mel he can sense evil , and says they should leave , but they are seized by guards . They are brought before Commodore Travers — whom the Doctor has met once before . Travers denies sending a mayday signal , but wants the Doctor and Mel to remain on board , and confines them to passenger quarters . Travers hopes ( from his previous experience of the Doctor ' s behaviour ) that he will be able to find out who sent the fake mayday call . The Doctor is convinced that whoever sent the message knew him and wanted him on board . Mel suggests that the Doctor ask for a passenger list , in the hope of spotting a familiar name , while she wanders around the large liner in hope of finding the mysterious contact . Security officer Rudge takes Mel to the ship ' s gymnasium , where he shows her how to use the headphones and tape recordings to help her exercise . While she is doing so , Doland arrives and informs Lasky that someone has broken into their hydroponics centre . As they rush off to find Bruchner , Mel hears someone on her headphones , telling her to take the Doctor to Cabin 6 . Down in the cargo hold , Lasky , Doland and Bruchner check the hydroponics centre ; the large pods inside are stable , but the Demeter seed s have been stolen from the small work cabin . In the lounge , the Doctor persuades the stewardess Janet to let him see the passenger list , but he does not recognise any of the names . Mel arrives and gives the Doctor the message to go to Cabin 6 , but the Doctor declines , claiming he feels like he would be simply walking into a trap . Mel decides to go by herself , but when she arrives , she discovers the Doctor is already there . They find the room has been wrecked , supposedly in a fight , and they find the silver Demeter seeds and a single boot . Rudge contacts Travers to inform him there has been an accident in the waste disposal unit ; it seems that someone has been thrown inside . All that is left is a boot matching the one found by the Doctor and Mel in Cabin 6 . They learn that these belonged to Grenville , but the Doctor does not recognise the name . The Doctor and Mel go to the gymnasium . The Doctor says that , with Grenville dead , there is nothing they can do . Mel departs to investigate the hydroponics centre alone . Back in the courtroom , the Doctor interrupts the display to claim that there have been changes to these scenes , and states that he is being manipulated . Mel enters the cargo hold , where she meets Edwardes . He agrees to show her the hydroponics centre . It was set up for the journey specially for Lasky , Doland and Bruchner , and that only low spectrum light is allowed inside to keep the pods dormant . When Edwardes tries to enter , he is electrocuted . Mel screams in fright , and sparks fly around the mysterious pods . . . Part ten . Two guards arrive at the scene , and Mel tells them that Edwardes is dead . One of the guards leads Mel away , and the other guard examines Edwardes ' corpse . Later , Doland and Bruchner arrive to find that all the pods have been opened . Bruchner looks on in horror , asking Doland if he realises what has been unleashed . Rudge brings the Doctor to the bridge to help question Mel about being in the hydroponics centre . Rudge then gets a message from the medical team that was sent down to the hold to collect Edwardes ' body , claiming that neither Edwardes nor the guard can be found . When Travers asks the Doctor what is going on — with a passenger , now Edwardes and a guard all gone missing , two , if not all three , murdered — Mel replies that a killer must be on board the ship . Travers decides to speed up their journey to Earth , and has the ship ' s course altered . He enters the lounge to inform the passengers that their arrival time will be brought forward by around 72 hours . Three Mogarians express their concerns that this will take them close to the Black Hole of Tartarus , but Travers assures them that they will be within adequate safety margins . Later , one of the Mogarians collapses after having a drink . The Doctor attempts to remove the figure ' s face plate , but the others protest that oxygen is lethal to a Mogarian . The Doctor believes it is not a Mogarian , and removes the face plate to reveal that is actually Grenville . The Doctor , however , recognises the man as Hallett , an undercover investigator . When Kimber recalls recognising Hallett before , in front of most of the other passengers , the Doctor guesses that Hallett has faked his own death to avoid being discovered . The Valeyard asks the Doctor how he knew the man was a fake . The Doctor replays the scene where the Mogarians spoke to Travers about the black hole , which shows that the fake one did not have his translator switched on . The Doctor also points out that Hallett ' s death meant that he could no longer play a passive role on board the " Hyperion III " . Mel realises that the Demeter seeds left in the wrecked cabin for her and the Doctor to discover were a clue to lead them to the hydroponics centre . They go down to the hold to have a look at the place , and the Doctor wonders what came out of the pods . Returning to the passenger quarters , they see Lasky leaving a guarded isolation room . They wonder what she was doing inside , so the Doctor sets off a fire alarm to distract the guard . He and Mel enter the room , where they find a half - human , half - plant hybrid strapped to a table . Mel screams in fright . . . Part eleven . The creature sits up and implores the Doctor and Mel to stop Lasky , but Lasky , Bruchner and Doland arrive and sedate her . Doland tells the time travellers that the creature is his assistant , Ruth Baxter . During their experiments involving cross - fertilisation , a speck of pollen penetrated a tiny scratch in Ruth ' s thumb , causing the resulting plant maturing process to partially transform her human body . They are taking her to Earth in the hope that they can reverse the infection . Mel hears a noise in the air conditioning ducts . Attaching one of the headphones to the grill , she uses the gym sound equipment to amplify the sound and record what she hears onto one of the music tapes . She overhears creatures planning to kill all the animal - kind on the ship . As she listens , she is attacked from behind and rendered unconscious with an anaesthetic . The attacker dumps her in a disposal trolley . The Doctor enters the gym and hears the recording , including her scream when she was attacked . The Doctor runs after the trolley and rescues her from being killed in the waste disposal unit . Unfortunately , the attacker has removed the tape . Bruchner is becoming increasingly hysterical about the situation with the hydroponics centre , especially when the elderly Kimber disappears . It turns out that he , Edwardes and the missing guard have all been killed by plant - like creatures called Vervoids — the creatures that came out of the pods when Edwardes was electrocuted . The Vervoids are slowly skulking through the " Hyperion III " s air ducts , secretly killing the crew and passengers one at a time and dumping their bodies in their lair . Lasky finds Bruchner burning the notes on their work in the hydroponics centre ' s small work cabin and tries unsuccessfully to reason with him about his actions . Bruchner knocks Lasky out , runs off and attacks a guard , taking his gun . He goes to the bridge and forces Travers and the pilot to leave , then changes the course of the " Hyperion " to head straight into the black hole of Tartarus — planning to destroy the ship , and the Vervoids with it . The Doctor informs the Commodore of the Hyperion III of this fact . Professor Lasky is stunned by this news . The Doctor looks accusingly at the Commodore . . . Part twelve . The Doctor , Lasky and Travers attempt to break into the bridge , but they discover it is filled with marsh gas . This has been released into the bridge by the Vervoids , who — having overheard Lasky talking with Bruchner in the hydroponics centre — have learned that they are the only members of their species . Bruchner is killed by the gas , but the ship is still heading into the black hole . Rudge summons the two Mogarians , as they can breathe in the poisonous atmosphere . They manage to direct the ship away from the black hole , but when it is safe , Rudge tells Travers that he and the Mogarians are taking over the ship . Mel gets to the lounge ahead of Rudge and warns Doland and Janet of the hijacking . Rudge tells the Doctor that the Mogarians are trying to regain the supply of metals stored in the vault , as they consider the expiring resources of rare minerals were stolen from their planet . Rudge himself is taking the hijacking as a means of securing a " more comfortable retirement " , as this Mogar - Earth journey was to be his last voyage as a security officer before being written off . On the bridge , an unknown assailant kills the Mogarians by throwing a liquid at them which damages their suits and causes them to die from exposure to an oxygen environment . Mel sneaks through the air ducts to let the Doctor know that the guards will attack the lounge . The Doctor believes this is too risky and tells her to attack the bridge instead . When they arrive , they find the Mogarians dead and take the face plates to prove to Rudge the hijack is over . Doland knocks the gun from Rudge ' s hands , and he runs into the corridors but is soon killed by the Vervoids . The Doctor tells Travers about the stolen tape recording and requests his permission to search the passenger cabins . While Mel checks Lasky ' s locker in the gym , the Doctor tells Doland that he thinks the traitor is either him or Lasky . After searching the professor ' s cabin , Doland suggests the cabinet in the hydroponics centre work cabin . There , Doland reveals the tape is in his pocket , but that he has wiped it . Taking the Doctor ' s gun , Doland admits the murders . He reveals that he plans to use the Vervoids for slave labour , taking over factories and farms from robots . However , the Doctor has disarmed the gun , and Travers arrives and arrests Doland . However , Doland and the guard are attacked and killed by the Vervoids . The Doctor , Mel , Travers and Lasky meet on the bridge to discuss the Vervoids . Lasky believes that something must have gone wrong with their DNA , but the Doctor tells them that the Vervoids ' hostillity towards them is instinctive : They are a form of carefully bred plant life , and all animal - kind ultimately consumes plant life . This means that the Vervoids hate animal - kind and kill for survival . Lasky realises that this is what made Bruchner so hysterical , and vows to help destroy the creatures , with Travers asking the Doctor to do the same . Back in the courtroom , the Doctor states that this shows he was not meddling , but had been asked to help . The Inquisitor accepts his argument , but the Valeyard wishes to see the outcome of events . In the hydroponics centre , Lasky finds that the necessary chemicals to create herbicide had been taken by the Vervoids . She , Mel and the Doctor are then surrounded by the plants . Lasky tries to reason with them , but they kill her and take her body back to their lair . Escaping through the air ducts , Mel and the Doctor discover the pile of bodies . The Doctor tells the distraught Mel that this is the Vervoids ' version of a compost heap . The Doctor has an idea that vionesium , the rare metal taken from Mogar and stored in the ship ' s vault , would accelerate the Vervoids ' life - cycle towards its natural end . Exposed to oxygenated air , vionesium releases intense light and carbon dioxide — to the Vervoids , the basic ingredients for their life - cycle induced by the seasons of spring , summer and autumn . Travers lowers the lighting and heating in the ship , forcing the Vervoids back to their lair , where the Doctor and Mel are waiting . They successfully deploy the metal against the Vervoids , which causes the creatures ' leaf - covered bodies to turn brown , wither , and die . Having saved the survivors , the Doctor and Mel bid their farewells to Travers and Janet , and depart in the TARDIS . Back in the courtroom , the Inquisitor asks the Doctor if any of the Vervoids survived , and he informs her that none did ; if even a leaf had survived and reached Earth , a Vervoid would have grown . Seizing on this , the Valeyard accuses the Doctor of destroying a entire species and for the punishment , the charge must now be genocide . . . Home video and audio releases . DVD release DVD Contents VHS releases