The Ribos Operation ( TV story ) The Ribos Operation was the first story of season 16 of " Doctor Who " . It began the season - long quest to find the legendary Key to Time . All four parts of " The Ribos Operation " ran over the allocated time , so a significant amount of material was cut for the broadcast version . Some of this material was retained in Ian Marter ' s novelisation . There was much debate as to whether K9 should return after the problems the prop had caused in season 15 . The character was popular with younger audiences so , with the assurance that the new prop was more efficient , Graham Williams approved the introduction of K9 Mark II . Tom Baker ' s lip was cut in an accident in which a dog bit him . This meant he had a visible sticking plaster upon his face in the publicity stills for this story . The scar from the injury remained visible in much of this and subsequent stories . " The Ribos Operation " was notable for seeing a number of debut appearances . It was the first serial to feature Mary Tamm as companion Romana I and was also the first to properly feature K9 Mark II . The White Guardian also made his debut . He was not seen again until " Enlightenment " , though his voice was heard in " The Stones of Blood " . Synopsis . The Doctor is summoned by the mysterious and powerful White Guardian , and sent on a quest to find the six segments of the Key to Time , which , once assembled , will restore balance to the Universe . Joining the Doctor and K9 is the smart and sassy Romana I , a Time Lord fresh from the Academy . Landing on the wintry planet of Ribos to locate the first segment , the TARDIS crew quickly find themselves embroiled in a little local trouble with a pair of con men and an unstable warlord . . . Plot . Part 1 . Using a dog whistle to awaken K9 , The Doctor begins busily planning a holiday to Halergan 3 . Suddenly , the TARDIS goes dark , and a mysterious voice summons him from outside . The White Guardian asks the Doctor to complete a task for him — to find the six segments of the Key to Time , an immensely powerful cube which maintains the equilibrium of time . The segments are hidden throughout the cosmos , though they can be found with a locator . Before the Doctor embarks on the quest , he is warned that there is a dangerous Black Guardian who also covets the Key . Returning to the TARDIS , the Doctor finds that he has been assigned a new assistant , a Time Lord named Romanadvoratrelundar , whom the Doctor calls " Romana " . As a new recruit from the Time Lord Academy on Gallifrey , Romana is inexperienced , but she believes herself just as capable as the Doctor , who would rather work alone . The Doctor , though incensed to find that there is now a hole in his console , inserts the locator in the hole and sees that the first segment is presently on Cyrrhenis Minima . . . at least , it is for a moment , before the coordinates change to new ones : Ribos , 116 parsec s away . Meanwhile , on Ribos , Garron and Unstoffe are atop a parapet of the castle of Shur that houses the planet ' s crown jewels . As guards in the vault extinguish the lights and secure the room , Unstoffe drops a chunk of drugged meat into the chamber , then lowers a ladder . Unstoffe reluctantly climbs down , stepping off the ladder next to the sleeping shrivenzale . Working quickly but quietly , he cuts a hole in the glass case housing the valuable jewels . Then , rather than steal anything , he places in a large piece of jethrik , a precious blue stone and the rarest and most valued mineral in the galaxy . Garron leaves to meet the Graff Vynda - K , an exiled tyrant . Shortly after they make their introductions and leave , the Doctor ' s TARDIS materialises and the two Time Lords emerge . As the Doctor is instructing Romana on the value of always expecting the unexpected , he is unexpectedly caught in a net . The Graff is impressed by the planet ' s supposed quantity of jethrik . Garron uses a bug in the Graff ' s chamber to monitor his conversation with Sholakh , the Graff ' s aide , but he is interrupted by the Doctor and Romana in the passageway . He effects the manner of a watchman to make his escape , calling out , " Four o ' clock and all ' s well ! " as he walks away . But the Doctor is puzzled by the fact that he does it with a Somerset accent . The locator points the Doctor and Romana to the chamber containing the jethrik and the Crown Jewels of Ribos . As the Doctor tries to open the locks to retrieve the segment , Unstoffe joins one of the guards atop the tower and gives him a drink , which conveniently knocks him out . Unstoffe blows the guard ' s horn , and the guards below lower the door to the shrivenzale ' s chamber — trapping the Doctor and Romana with the waking beast . . . Part 2 . The guards operating the door notice the obstruction and , fearing harm to the shrivenzale , lift it again , freeing the Time Lords . The door is soon closed , keeping the shrivenzale at bay . The Doctor and Romana hide when guards enter the room , followed by Garron , who asks for a substantial sum of money to be kept there for protection . The Doctor is concerned he may also be after the segment . The money will , of course , be the Graff Vynda - K ' s deposit for his purchase of the planet , which he intends to use as a base to build an army and a battle fleet . The Graff is intrigued when Unstoffe , pretending to be a native of Ribos , concocts a tale about a lost mine containing an excess of jethrik . He sends Sholakh for his money , then discovers the bug planted in his chamber . He realises that Garron is trying to con him . Later , Unstoffe distracts the shrivenzale , recovers their piece of jethrik , and takes the money from the safe . By now , the Doctor has realised that the piece of Jethrik is the segment . He also tries to take it , but the guards are alerted , prompting him to escape using Unstoffe ' s route while Unstoffe bolts through the door with the jethrik . However , an angry Graff , who intends to kill them for deceiving him , intercepts the Doctor , Romana and Garron . He orders their execution on the spot . . . Part 3 . Distracted momentarily by the Doctor and advised by Sholakh to remember the money stolen , the Graff instead takes Garron prisoner with his presumed accomplices , the Doctor and Romana . The Graff confronts the Shrieve captain to see what is being done . Noticing the jethrik is gone as well , he discovers the " scringestone " tale is a lie . Meanwhile , Sholakh discovers that Garron has an accomplice when his communicator begins beeping . After Sholakh leaves , the Doctor uses his dog whistle to summon K9 . Unstoffe hides with Binro , a homeless outcast who believes that Ribos is a planet orbiting a star , which Unstoffe confirms to be true . The Ribos guards summon the Seeker , who locates Unstoffe ' s hideout . The guards prepare a pre - dawn raid . The Graff has other plans and orders Sholakh to rally his men , go in to massacre all the Ribosians , take the jethrik and leave . Using the listening device in the Graff ' s room , Garron warns Unstoffe about the Graff . While the Seeker and the Graff are in the concourse , Binro , thankful for Unstoffe ' s encouragement , leads him to the labyrinthine catacombs under the city . K9 helps the Doctor , Romana and Garron escape from the Graff ' s quarters . The Graff and his men enter the catacombs without the Ribos guards , who fear the place as the home of the Ice God s . Binro and Unstoffe don ' t fear the Ice Gods , knowing they are mythical , but they do fear the nest of shrivenzale s they hear in the distance . The Doctor ' s group is not far behind them , but they are forced to hide when the Graff ' s party comes upon them . Unfortunately , the Doctor gives away their presence when a skull falls to the floor . . . Part 4 . The noise of the skull also draws the attention of a shrivenzale , scattering the Graff ' s men . Reflecting on the difficulty of finding their quarry , Sholakh advises the Graff to use the Seeker as her earlier information was accurate . The Doctor sends the rest of his group ahead and doubles back to the city . Farther down in the catacombs , Unstoffe and Binro split up , the latter also doubling back to see if he can determine Garron ' s fate . Unstoffe gives Binro his communicator to demonstrate to Garron that it isn ' t a trick of any sort . At the entrance to the catacombs , the impatient Graff kills one of the guardsmen in front of the Shrieve captain to convey his displeasure with being made to wait for the Seeker . After witnessing this display of ruthlessness from a hiding place , the Doctor returns to the Graff ' s chambers . There , he stands over the fallen soldier whom K9 had earlier incapacitated . Garron steals the core to the Key to Time from Romana and heads off to locate the jethrik and Unstoffe , in that order . The Seeker , meanwhile , foresees that if they enter the catacombs , " all but one " of the party will die . Nevertheless , she leads the Graff and his men into the catacombs . They encounter Binro , whom they mistake for a grave robber . Seeing he has Unstoffe ' s communicator , they take him with them to assist in finding Unstoffe . They proceed deeper . As they head off , the tail of a scarf peeks out from the robe of the last guard in line . . . The Graff corners Unstoffe and Garron . Binro runs to try to warn them and is shot dead . He dies content in the knowledge that he was right about his measurements of the stars . Unstoffe , upset , moves towards the Graff and is wounded . Garron bluffs the Graff by claiming the Doctor and Romana are interstellar agents , who have stumbled across the Graff ' s crimes while they were arresting Garron . This only serves to enrage the Graff further . Unnoticed by all , in all this activity , is one of the Graff ' s guards , blowing a dog whistle . Adding to the chaos , a shrivenzale draws near . The Ribos guards use a cannon to destroy the entrance to the catacombs , causing the ceiling to collapse on the Graff ' s men . The collapse traps Unstoffe and Garron , but they are freed by K9 . Romana reclaims the tracer that Garron stole . The Graff notices that Sholak is trapped and tries to save him , but it is too late . With the money and the piece of Jethrik , the Graff recalls the Seeker ' s prophecy that all but one of his group will die . He kills the Seeker to make sure that he will be the only one who survives . His last surviving guard moves towards her as she is killed , but the Graff announces that his guard will receive a more honourable death . He gives the guard an explosive to kill himself with . The guard , actually the Doctor in disguise , swaps the explosive for the Jethrik . The Graff walks off into the maze yelling for Sholak before exploding . After leaving the catacombs , Garron and Unstoffe are free to commandeer the Graff ' s deserted ship . The Doctor , Romana and K9 depart in the TARDIS , and the Doctor and Romana reveal the first piece of the Key to Time . The Doctor looks at the first segment and comments , " Only five more to go . " Story notes . Production errors . " to be added " Home video and audio releases . DVD releases . Extras ( 2007 / 2009 version ) : Notes : Doctor Who DVD Files . It was released as issue 107 of " Doctor Who DVD Files " .