Domain of the Voord ( audio story ) Publisher ' s summary . The Doctor , Susan , Ian , and Barbara land on the planet Hydra , where Admiral Jonas Kaan leads a vast flotilla of ships trying to elude the vicious race that has invaded and occupied their world . But his ships are being picked off one by one , vessels , and crews dragged underwater by an unseen foe . The time travellers find themselves pitched into battle against the Voord , the ruthless enemy they last encountered on the planet Marinus . As they take the fight to the very heart of the territory now controlled by the Voord the stakes get higher . First they lose the TARDIS . . . then they lose that which they hold most dear . And that ' s only the start of their troubles . In the capital , Predora City , they will learn the truth of what it means to be a Voord . And that truth is horrifying . Plot . The Floating City ( 1 ) . When the TARDIS lands on a cargo ship called the " Hopeful " , the First Doctor , Ian , Barbara and Susan are discovered by the crew . Suspecting them to be spies , Pan Vexel and Amyra Kaan take them to the " Fortitude " , the ship at the head of an entire flotilla . On the bridge , Admiral Jonas Kaan , Amyra ' s father , speaks with the TARDIS crew . He tells them they are on Hydra , a planet completely covered by an ocean save for one landmass — the continent of Predora . Predora City was where the Hydran s lived before the planet was invaded a year before . As they speak , the flotilla alarm blares out . The " Hopeful " has been sunk and with it , the TARDIS . The crew jump into the ocean but are pulled under . Amyra notes that although similar attacks have happened before , this is the first such attack that has been carried out during the day . One of the crew picks up a contact on sonar . To identify the source , a diving squad is formed and Ian volunteers . Once under the water in a diving suit , he spots a bullet - shaped submersible being piloted by a Voord . When Kaan learns the travellers have encountered and defeated the Voord before on Marinus , he tells them they will be of more help than he had thought . The Voord fires a wire at one of the divers and drags him away . Ian is separated from the other divers , then spots around fifty more Voord submarines emerge from the darkness of the ocean floor and they begin firing torpedoes at the fleet . One of them hits the " Fortitude " and the Doctor takes over for the unconscious sonar operator . A depth charge is dropped at a large cluster of Voord submersibles , taking most of them out , but the rest head for the " Fortitude " . The ship comes under more fire . Kaan calls for an evacuation . The Doctor agrees to stay with the Admiral under another torpedo knocks Kaan unconscious . Barbara and Susan help him to the lifeboats but the Doctor stays to keep contact with Ian . Ian is rammed by a Voord submersible but he grabs hold of it , although his lifeline snaps . As Barbara returns to the bridge to collect the Doctor , Ian is able to influence the direction of the submarine . When they surface , the Voord attacks him with a knife but Ian knocks him out in their struggle . Afterwards , he sees the " Fortitude " sinking . The Doctor and Barbara are still trapped inside as water rushes in through the windows . Susan and Amyra also witness the sinking from the lifeboat . Susan reduced to tears as she has to face the fact that the Doctor and Barbara are gone . Return to Terror ( 2 ) . The Voord withdraw after the " Fortitude " sinks . A quarter of the flotilla is gone and few Hyrans who went into the water were saved . Some days after the attack , Ian speaks with a grieving Susan . She laments that with the loss of the Doctor , Barbara and the TARDIS , Hydra is now their home . She had thought they saw the last of the Voord on Marinus but Ian says that Yartek and his followers were but one group ; Hydra is facing a full - scale invasion . The Voord Ian fought has been taken prisoner and remains captive in a cell but has said nothing and Vexel is watching him to make sure other members of the crew don ' t try to murder him in anger . Kaan recovered and they now have a new flagship called the " Vigilant " , a lesser warship than the " Fortitude " . They head for Predora City in hopes of rallying some of the resistance groups . Ian is asked to have a hand at interrogating the Voord prisoner . Ian tells him of his history with the Voord . The Voord speaks , giving his name as Nebrin and expressing some familiarity with Yartek ' s expedition . But he warns Ian that Hydra is not Marinus . The Voord rule here and soon everyone will be " harvested " . He says no more and Ian leaves . The ships set off on a long journey towards Predora . During that time , Susan speaks with Nebrin . She addresses him in a far friendlier manner than everyone else , despite the Voord dismissing all the death they caused as a consequence of war . Nebrin claims the Voord invaded Hydra to bring the Hydrans the " gift " of Voord leadership . He tells Susan she may speak with him again later if she wishes and after she leaves , Nebrin chuckles quietly to himself . Amyra meets Ian who has volunteered for night - watch . Amyra tells Ian about how she lost her mother and brother in the occupation . She inquires about the TARDIS and Ian tells her it was a time machine and , despite her giggles , Amyra believes him . Meanwhile , Susan speaks with Nebrin again about her grandfather and Barbara . Nebrin tells her that his father was a teacher just like Barbara . Before Susan can ask more , she is found speaking to Nebrin and taken away . Suspicious and angry , Ian forbids Susan and Nebrin from speaking again . Alone , Nebrin says she will be harvested . After some months of travelling , the flotilla enters Voord territory and as they close in on Predora City , it seems quiet . They spot an unusual dome building , presumably constructed by the Voord , rising out of the water but they decide not to investigate and instead follow their original objectives . Scout ships report that the streets are empty . The Admiral prepared a party of troops to venture towards the Autumn Palace , Predora ' s centre of government , while Vexel is left in command of the flotilla . Ian and Susan willingly join the landing party and Nebrin is taken along too for use as a hostage . When they arrive at the palace , the Voord reveal themselves in their hundreds and with the captain s of the ships that did not join the convoy to Predora months earlier in their capticity . The landing party surrenders . Nebrin , being a Voord commander , takes charge summons the rest of the Voord and thousands of them emerge from the buildings of the city below the palace . The ships were also overrun but Vexel surrendered to avoid bloodshed . Nebrin announces that Predora City is now the domain of the Voord . Nebrin then takes Ian , Susan , Kaan and Amyra back inside the palace and out into the garden where he reveals that the Voord are in possession of the TARDIS . Two Voord submersibles caught it before it sank to the seabed but they have been unable to gain access . They seem confident that Susan will teach them how it works soon enough however . Suddenly a group of armed Hydrans resist the Voord and charge into the garden firing their weapons . As the Voord fight back , Kaan and Amyra usher Ian and Susan inside the TARDIS . They urge them to take the TARDIS away to prevent the Voord from discovering the secrets of time travel . From the scanner the time travellers watch the Hydrans run from the Voord but only Amyra escapes over the garden wall . The others , including the Admiral , are all shot . The Voord then surround the TARDIS and order Ian and Susan to exit the craft . Although Susan tries to protest , Ian sees taking the TARDIS away from Hydra as the best option and he sets the ship in flight . Behind the Mask ( 3 ) . Susan stops Ian before take - off can properly commence . She thinks the Doctor and Barbara are alive . She heard Nebrin refer to him as " the Doctor " but when she was speaking with him , she only ever called him " Grandfather " . Thus she has concluded that Nebrin knew he was called the Doctor by communing with other Voord , and these other Voord must have known he was called the Doctor by communicating directly with him or Barbara . Ian thinks Susan may be right and agrees to stay . They give up and Nebrin has them separated . Susan is allowed to hold on to her TARDIS key so the Voord may access the ship later . Ian is put in a cell with other Hydrans , some of them members of the landing party . Among them is Jonas Kaan . Those that were shot by the Voord were only stunned as they were required for the harvest . They are being held prisoner until they can be indoctrinated to accept the Voords ' life view . Ian tells Kaan the Doctor and Barbara may still be alive and somewhere in Predora . They spy a small window in the cell and through it Ian sees a huge airship landing in the square below the Autumn Palace . Out of it steps Overlord Tarlak who expressed his displeasure with Nebrin for being captured , bringing the Voord operations to near disaster , though Nebrin defends his decisions to attack the flotilla which was ultimately successful . Tarlak communes with Nebrin to learn more about what has happened before he arrived . Tarlak later addresses Susan in the Palace and asks her how she can have defeated Yartek on Marinus when those events happened a hundred years prior . Susan instead asks about Ian , Barbara and the Doctor . Tarlak claims she will have no need of that family any longer — the Voord will be her family . They call forward Vexel who has been an agent of the Voord since the first week of the invasion . It was he that sent messages to the Voord to allow them to launch such a successful attack on the Hydran Navy when the TARDIS crew first arrived , and he also placed a tracking device on the TARDIS to signal to the Voord to capture it before it sank . Tarlak now prepares to reward Vexel with " a public demonstration of what it means to be Voord " . In the square , the assembled prisoners watch as Tarlak presents Vexel with a Voord mask . The mask alters the wearer ' s genetic code and becomes part of them , turning them into a Voord . However the wearer must be fully committed to the Voord and accept the transformation , otherwise the mask rejects them . Removing the mask can result in horrible disfigurement , if not death , as it becomes a part of the wearer . Tarlak places the mask over Vexel ' s head and he becomes a Voord . This is the plan the Voord have for all Hydrans , and those that reject it will become slave s for a time and be killed before the year ' s end . Many have already become Voord . Tarlak and Nebrin leave with Susan to inspect the sea engine . Ian , Kaan and the other prisoners are led to the dome building by the shore and are set to work digging away rock s restricting access to the site . Tarlak ' s airship flies above the dome and a capsule carrying Tarlak , Nebrin , Susan and two guards is lowered inside . The building is for generating power with a type of hydroelectric dynamo . Tarlak does not tell her what they use the power for . He sends Nebrin away to inspect the slaves but before he leaves Nebrin warns Susan to be careful , as Tarlak is becoming impatient with her . As they leave the dome , a hidden attack begins and the slaves take the opportunity to flee . Those that make it encounter Amyra and other Hydran rebels . Susan is taken to the slave deck of Tarlak ' s airship . After comforting a crying woman , she hears an old man and makes out some familiar features in the dark . But when she gets close enough , she screams as she finds the man ' s face scarred and disfigured , caused by the removal of a Voord mask . A voice tells her he is not the Doctor . Susan is elated to see Barbara again but her spirits do not remain high after Barbara tells her the Doctor is dead . Fightback ( 4 ) . Barbara explains that when the " Fortitude " sank , it broke apart , allowing her and the Doctor a small gap of time to swim out of the wreckage , but then the Voord captured them . From what Barbara heard afterwards , Voord physicians failed to give the Doctor adequate medical treatment and he died . Elsewhere on the airship , Tarlak and Nebrin discuss the recent attacks . The rebels are gaining victories in the provinces . Tarlak is sure someone is giving them tactical advice and he has some idea of who it might be — the Doctor . The Overlord tells Nebrin the Doctor ' s body shut itself down when near death , then he woke up later and escaped , which coincided with the upsurge in rebel attacks . Tarlak convinced Barbara he was dead to avoid giving hope to the resistance . Nebrin is shocked to learn that Tarlak had the Voord physicians executed . Tarlak makes nothing of it and decrees that as the Doctor and Susan are of a fantastically advanced race , they must be harvested . As they speak , a man named Tarn leads the escapees into a cavern where the meet the Doctor . The Doctor details his plan to destroy the Voord sea engine , which they plan to use to enhance their telepathic powers , before construction is completed . At present , these powers are being stretched thin by the sheer number of Voord in the vicinity . He sends a message all over Predora , rallying the Hyrans in preparation for a huge rebellion against the Voord . Tarlak responds to the message by threatening to place a Voord mask onto Susan . Nebrin tries to convince Susan to accept the Voord conditioning as it is the only way to save her life . He is opposed to Tarlak forcing Susan to wear the mask , which goes against Voord customs , but sees no way he can stop the Overlord . Kaan and Amyra lead an attack on Predora City . This leaves the sea engines lightly guarded and the Doctor and Ian enter with a smaller party . Nevertheless they encounter Vexel who has the Doctor watch Susan receive the Voord mask on a screen . However , Nebrin knocks the mask out of Tarlak ' s hands and denounced his actions for dishonouring the ritual and being no more than murder . Tarlak subjects Nebrin to a mental onslaught , killing him . Fortunately these events distract Vexel and Ian tackles him . Their fight ends with Vexel falling into the generator . The Doctor uses the sea engines to send a pulse wave through the city , severing the mental connection between the Voord commanders and their footsoldiers , rendering them harmless , and to prevent them from repairing the connection , the Doctor blows up the sea engines . Tarlak is retrained by the now free Hydrans . The war on Hydra is not over but now all that remains is to capture the Voord commanders in the provinces , who are now without their footsoldiers . Kaan becomes the President of Predora and Amyra succeeds him as Admiral . They say their farewells to the TARDIS crew and inform them that the Voord will face galactic justice . After wishing the Hydrans good luck , the TARDIS dematerialises . As Kaan and Amyra think about where the travellers are going , the TARDIS has already taken them several galaxies and thousands of years away .