Meglos ( TV story ) Meglos was the second serial of season eighteen of " Doctor Who " and the second serial in the John Nathan - Turner era . It featured Jacqueline Hill ' s return to the program for the first time since the " Doctor Who " story " The Chase " in 1965 . The serial also afforded Tom Baker a chance to take on both villainous and heroic roles in the same story , as William Hartnell and Patrick Troughton had and Peter Davison and Matt Smith would . ( TV : " The Massacre of St Bartholomew ' s Eve " , " The Enemy of the World " , " Arc of Infinity " , " Nightmare in Silver " ) " Meglos " came into being after Christopher H . Bidmead purposefully sought out John Flanagan and Andrew McCulloch as new talent . Nathan - Turner was unimpressed with the ideas put forward and the serial was shuffled to various placements in the season , largely because it didn ' t feature Adric . Behind the scenes , " Meglos " was highly innovative as the British Broadcasting Corporation ' s first use of Scene Sync , a motion control technology that improved the believability of composite shots that used CSO . It would be the only " Doctor Who " serial to avail itself of the technology . Nevertheless , other BBC productions would use Scene Sync based on this successful test , such as Barry Letts ' , starring Elisabeth Sladen . ( DOC : " The Scene Sync Story " ) Synopsis . On Tigella , two opposing factions are irrevocably divided over one fundamental issue : the Dodecahedron , a mysterious artefact which provides the entire planet ' s energy . With the Savants and the Deons locked in a crippling stalemate , and their civilisation on the brink of collapse , the Tigellan leader Zastor seeks the Doctor ' s help . But the Doctor and Romana have been trapped aboard the TARDIS in a timeloop by Meglos , the last of the Zolpha Thurans , who will stop at nothing to steal back the awesome power of the Dodecahedron . Plot . Part one . In the TARDIS , the Fourth Doctor and Romana are repairing K9 yet again . They hover near the planet Tigella ; the Doctor recalls an earlier visit when he befriended a man named Zastor , leader of the Tigellan s , and decides to get in touch with him . On Tigella , a power loss occurs when a transformer breaks down . The inhabitants , living under the surface , find it hard to compensate . Arguments continue between the Deon s and the Savants over ownership of the Dodecahedron , Tigella ' s power source and the Deons ' deity . The Deons refuse the workers access to the Dodecahedron . Zastor , unable to decide , orders the Doctor sent for . Deedrix leads the workers in the belief that the Dodecahedron is merely an artefact ; Lexa , leader of the Deons , holds firm in her faith that the Dodecahedron is a god . On Zolfa - Thura , a ship touches down . A party of Gaztak s led by General Grugger emerge . They bring forth an Earthling , whom they stun . They brought him to the planet on the promise of reward . A hidden structure emerges from the ground . A door opens and the party enters . Within is Meglos , a Zolfa - Thuran . Meglos outlines his plans to the Gaztaks . He wants them to have the Dodecahedron to power the galaxy . He tells them of the recent power fluctuations the Tigellans have been experiencing . The Earthling and Meglos are placed in adjacent chambers . Grugger plans to steal the machinery , but Meglos traps him and his aide , Brotadac , in the room . They agree to comply with his plan . They then transfer Meglos ' consciousness into the Earthling . His skin becomes cactus - like in appearance . Claiming the Doctor is a threat , Meglos traps him in a time loop . As Meglos turns around , it appears he has taken on the Doctor ' s appearance . . . Part two . Onboard the TARDIS , the Doctor and Romana continue around the loop . Their only respite is a small period of freedom between the loops . Meanwhile , Meglos leaves with the Gaztak s in their ship . On Tigella , Lexa tells Zastor that she will allow the Doctor access to the Dodecahedron if he swears the Deon oath . Outside , the Gaztak ship lands . The Gaztaks stay with their ship whilst Meglos enters the Tigellan city and introduces himself . The Doctor and Romana break the loop by performing the actions before they happen , freeing themselves . Meglos swears allegiance to Ti in the Deon ceremony . He tells the Tigellans that it is not safe for them to remain near as they are not Time Lord s like him . They agree to leave him to work alone . Meanwhile , the TARDIS lands on Tigella and the Doctor and Romana emerge . They are crossing the ground to the city when Romana is attacked by Bell Plant s . The Doctor and K9 continue on their way , unaware of her troubles . Meglos inspects the Dodecahedron and places a device on it . Lexa and Caris hide outside , having stayed behind to secretly observe the goings on . After Meglos leaves , they enter to find the Dodecahedron gone . The Doctor and K9 arrive at the Tigellan city . The guard tells him he didn ' t see him leave . Confused , the Doctor shrugs it off . He orders K9 to find Romana after noticing her absence . Meanwhile , Romana frees herself from the plants . She notices scorching on some of the vegetation . Lexa and Caris report their finding to Deedrix and Zastor and order the capture of the Doctor . The real Doctor is taken prisoner . Romana stumbles upon the Gaztak ship , and finds it responsible for the burning . The Gaztaks notice her and she runs . K9 heads back to the city as his batteries run low . The Gaztaks corner Romana and Brotadac orders her death . . . Part three . Grugger grabs Romana and questions her as to her origins . She tells him that he wouldn ' t believe her . Grugger orders her to lead him to her craft . In the city , Deedrix and Caris speculate on the Dodecahedron ' s disappearance . An announcement informs them that the power loss has reached critical . This means the city will collapse . Outside , Romana leads the Gaztaks in a circle back to their own ship . The Tigellans try to stop the damage . They have two hours to prevent the collapse . Lexa and Zastor question the Doctor and he realises they see him as the thief . Meanwhile , Romana convinces the Gaztaks to give her another chance to take them to her ship . Zastor agrees to allow the Doctor to see the power room . Meglos is harassed by the Earthling he took over , who is fighting him . Meglos approaches Caris and tells her she will obey him . He shows her an impossible thing to prove his power , the shrunken Dodecahedron . Lexa returns to her Deons and gives them orders . The Deons stage a revolution . They capture the Doctor , Zastor and Deedrix in the power room . Lexa proclaims that , to pacify Ti , all non - believers will be sent to the surface . Lexa tells Zastor that his belief was only words , not actions , and he is be be exiled . Lexa tells the Doctor that he is to be prepared for sacrifice . Outside , Romana leads the Gaztaks to the Bell Plants . Stamping on a root , she instigates an attack and runs away . The city doors begin to close . Romana finds K9 in a bush and carries him inside . The Gaztaks break free but are too slow to get indoors . Caris tells Meglos that he cannot escape but he disagrees , telling her there are ventilation shafts . He is again troubled by the Earthling . Though distracted by this , Caris pulls a gun on him and leads him through the city . The Gaztaks batter down the door and fight with the Tigellans . The Gaztaks force the Tigellans back . Romana sees Meglos , whom she thinks is the Doctor . She hits Caris , dazing her , and Meglos runs away . The Gaztaks ransack the city and Grugger kicks K9 , calling him " useless " . Caris tells Romana that it was not the Doctor she saw . Meglos emerges from the city and talks to Grugger , showing him the shrunken Dodecahedron . Meanwhile , Lexa continues her ceremony , hoping the sacrifice of the Doctor will return the Dodecahedron . The Gaztaks and Meglos board their ship again and prepare for take off . Romana and Caris begin to search for the real Doctor . A large stone hangs above the Doctor . It is suspended by three ropes . A Deon burns through two of them . He moves to the third . . . Part four . Zastor and Deedrix meet up with Caris and Romana . The Deons guarding the former are told of the attack and head for the surface . The new party heads for the power room . They rush in and Deedrix grabs the flaming torch from a Deon , preventing him from burning the final rope . Zastor and Romana tell Lexa of the Gaztak attack and that Meglos was the guilty one . On their ship , the Gaztaks and Meglos approach Zolfa - Thura . Meglos promises Grugger and Brotadac all the power they wish . The Doctor questions Meglos ' motives in taking the Dodecahedron to Zolfa - Thura . Romana reminds him of the screens of Zoltha - Thura and he concurs . Back on Zolfa - Thura , Meglos buries the Dodecahedron in the ground with the boundary of the Screens of Zolfa - Thura and activates it . The Dodecahedron rises atop of Meglos ' room . On Tigella , the Doctor and Romana bid farewell to the Tigellans before heading back to the TARDIS . However , as they leave , an apparently dead Gaztak rises and shoots at Romana . Lexa takes the shot . She falls , injured , and Romana rushes to her aid . The Doctor tells her they must leave , and Romana grabs K9 and follows him . Caris and Deedrix go with them . Meglos tells Grugger and Brotadac that the Dodecahedron can be amplified by the screens to fire a beam capable of destroying planets . He asks them to choose a planet to be destroyed and Grugger picks Tigella , angered by the loss of life . The Dodecahedron powers up as the TARDIS lands nearby . The Doctor decides to trick the Gaztaks by pretending to be Meglos . He leaves the others with the TARDIS . In the room , Meglos takes of his coat and heads out to check the screen ' s alignment . The Doctor sees him and takes his own coat off . Grugger decides he no longer needs Meglos and tells Brotadac he can wear the Doctor ' s coat as he always wanted to . The Doctor enters and interrupts them . He stalls the countdown , telling them preparations need to be made . A Gaztak walks in carrying the real Doctor ' s coat . The Doctor tells Grugger it is a present for him . Grugger is unimpressed and pressures him to activate the Dodecahedron . Outside , Romana , K9 , Caris and Deedrix decide to have a closer look at the screens . The Doctor tells Brotadac that the screens require two minutes to power up . He heads outside . Grugger tells Brotadac to take the Doctor prisoner , deciding that he can be kept in their spacecraft as he is no longer needed . Brotadac instructs two Gaztaks to capture him . The Doctor hides and they take Meglos prisoner . However , Brotadac and some Gaztaks find the real Doctor and capture him also , still believing him to be Meglos . The take him to their ship . Romana and her party see the Doctor being taken in . The Doctor is thrown in with Meglos . He tells Meglos that he has inverted the controls so that the Dodecahedron will destroy Zolfa - Thura and all on it . K9 distracts a guard posted to the Gaztak ship . Deedrix tries to knock him out so K9 shoots him . They then rush inside . K9 begins to cut down the door to the Doctor and Meglos ' cell . Deedrix and Caris detain Meglos but he exits the body , leaving the Earthling behind . He shuffles out of the ship . Grugger and Brotadac begin the countdown . At zero the beams will converge and the Dodecahedron will activate . The Doctor , Romana , K9 , Caris , Deedrix and the Earthling leave in the TARDIS . Meglos enters the room and returns to his cactus form . Grugger realises that something is wrong but is unable to stop it before detonation . The Doctor returns to Tigella where he bids farewell to Zastor . Romana informs the Doctor that Gallifrey wants them back immediately . The Earthling , initially wary of returning home since he told his wife he ' d be back home much earlier , agrees to let the Doctor take him back in the TARDIS . Story notes . Filming locations . " to be added " Home video and audio releases . VHS Release . This story was released on VHS in the UK in March 2003 . DVD Release . It was released on DVD on the following dates : DVD extras include :