The Pirate Planet ( TV story ) The Pirate Planet was the second story in season 16 of " Doctor Who " . It was the second story in the Key to Time arc . " The Pirate Planet " was the only transmitted story for which Douglas Adams received sole on - screen credit . It was also the latest serial of the " classic " era to be novelised , only receiving this treatment on 5 January 2017 . Synopsis . The Doctor and Romana I learn the second segment of the Key to Time is on the planet Calufrax . Yet they arrive on a planet called Zanak , which has been hollowed out and fitted with hyperspace engines , allowing its insane , half - robot Captain to materialise it around smaller planets and plunder their resources . Plot . Part 1 . On a mountain base , the nervous Mr Fibuli informs the impatient Captain that a new source has been found for vasilium . Immediate orders to mine it follow . The Captain speaks to the people of the planet , declaring a new golden age . As the people celebrate , a different group , dressed in yellow robes , mentally watch Pralix , who doesn ' t appear as thrilled with the Captain ' s announcement as everybody else . In the TARDIS , the Doctor is securing the first segment of the Key to Time by tucking it in a boot and sticking it in the fridge . The tracer points Romana I and him to the cold and boring planet of Calufrax . The TARDIS is unable to materialise ( damaging Zanak ' s engines as well ) until Romana pilots it into a landing . The pair soon discover that they are not on Calufrax at all . Meanwhile , Pralix is now delirious , watched over by his grandfather Balaton , sister Mula and friend Kimus . Balaton is concerned that his rantings will be overheard . The area in which the Doctor and his entourage have landed is deserted until they meet a local who tells them that the people of his planet are going to be rich because of the Captain and his latest " golden age of prosperity " . He gives Romana some diamond s and rubies , saying they can be found everywhere . He warns the Doctor and her about the Mentiad s , then leaves before he can elaborate . The Doctor finds precious stones all around , including the extremely rare oolion . Balaton is terrified that Pralix will be taken by the Mentiads . Kimus is sceptical , and Mula remembers her father ' s death at the hands of the Captain ' s guards , ostensibly to save him from the Mentiads . Meanwhile , the Mentiads declare their " harvest " of Pralix is imminent . As they march across the fields of Zanak , the Doctor hears Pralix and sets off to investigate . Romana waits behind , surveying the Captain ' s fortress with a telescope , only to be arrested for that forbidden item and her forbidden question : " Why ? " The Captain sends more of his soldiers to stop the Mentiads , but weapons are useless against their psychic powers . Instead , the Captain sends troops to find the telepath and eliminate him . They burst in on the Doctor in Pralix ' s home , but K9 quickly stuns them . The Mentiads enter soon after and strike down the Doctor with a blast of mental energy . . . Part 2 . When the Doctor wakes , Pralix and the Mentiads are gone . K9 tells him of Romana ' s arrest , giving him an incentive to try to get to the bridge atop the mountain , where she has been taken by the guard . Kimus accompanies him , hoping to rescue Pralix from the Mentiads . They get up to the mountain in an air car . Meanwhile , Mula and K9 track the Mentiads in an attempt to find Pralix . On the bridge , Fibuli breaks the news to the Captain that the macromat field integrator has burnt out and they cannot replace it themselves . He suggests one more jump to find mineral PJX 1 - 8 , which would do the same job as the integrator . Romana is brought to the bridge , and the Doctor also finds his way up . The Captain isn ' t taking any chances . He has guns trained on them as he encourages them to lend technical assistance . Romana is confused that the tracer gives out a continuous signal wherever they go . The Doctor realises what ' s going on . After they escape with Kimus and make their way underground , they find the ground beneath them is frozen . The Doctor explains the planet they are on , Zanak , has been hollowed out and fitted with engines so it can transmat through space and materialise around others — such as Calufrax — to plunder their mineral wealth . They have no time to pause as the Captain ' s guards give chase from behind . As they run , they face a group of Mentiads . Part 3 . There is no danger . The Mentiads are friendly . They have come to save the Doctor and his friends from the guards . The Mentiads , now including Pralix , create a force field with their psychic powers . This power of the Mentiads will not last much longer . Zanak has come to Calufrax for its crystals . When refined , they can be used to block their psychic abilities . The Doctor doesn ' t know it yet , but the Captain is planning to materialise Zanak around Earth after mining on Calufrax is finished , because mineral PJX 1 - 8 ( quartz ) has been located there . The Mentiads tell the Doctor that Zanak was a prosperous planet until the reign of Queen Xanxia , who supposedly had mysterious powers . Galactic wars she waged were the ruin of Zanak and its people . The Doctor and Kimus fail to steal an air car and are taken to the bridge . The Captain shows the Doctor his trophy room of crushed remains of planets . The Doctor ' s secret plan is to break into the engine room , but while looking for it , Kimus and he find a room with an old body connected to a time dam , used to slow down the flow of time , using the energy Zanak acquires to keep Queen Xanxia barely alive . The Doctor returns to the bridge and exposes the Captain ' s nurse as a hologram controlled by Queen Xanxia . The Queen believes that she has made her hologram nearly real . The Doctor tries to convince her that the escalating energy needs of the time dam she is using will eventually cause her real body to die . He is thrown overboard for his troubles . Part 4 . The Doctor survives because it was only a projection of him that walked the plank . He has figured out the final piece of Queen Xanxia ' s puzzle , the device he found in the room with the body . Xanxia has been using the device to create an image for herself , disguised as the Captain ' s nurse . Xanxia is almost immortal because of the power of Zanak , which she uses to give permanent form to her image . The Mentiads approach the bridge . They expect the Doctor to have taken control of the engine room by now , but because of the psychic interference transmitter , they are disadvantaged . The Captain seals the bridge as Zanak prepares to make the jump to Earth . Since Zanak ' s engines were damaged when the planet materialised in the same place as the TARDIS , the Doctor escapes and tries to employ the trick again to prevent Zanak from materialising , while the Mentiads do their best to sabotage Zanak ' s engines . Xanxia kills the Captain , who is saddened when Mr Fibuli dies , when he finally turns against her . The Doctor , Romana and the Mentiads destroy Zanak ' s bridge and Queen Xanxia , ending the devastation caused by Zanak ' s travels . In the aftermath , the Doctor and Romana collect the second segment of the Key to Time , the remains of Calufrax . They set off back to the TARDIS to search for the next segment . Story notes . Production errors . " to be added " Home video and audio releases . DVD releases . Contents ( 2007 / 2009 version ) : Notes :