Goodbye , Sarah Jane Smith ( TV story ) Goodbye , Sarah Jane Smith was the sixth and final story in the fourth series of " The Sarah Jane Adventures " . In a sad case of irony , due to the title and plot , it is the final story of the programme to be broadcast during the life of its star , Elisabeth Sladen . The story introduced a pair of foil characters to Sarah and Mr Smith , Ruby White and Mr White , and dealt with Sarah ' s quiet fear of growing too old and ill to continue protecting the Earth , becoming purposeless . It also revealed how deeply Luke ' s departure to Oxford had affected her . It was the last story in any media to feature K9 Mark IV . The character would continue to make appearances in invalid material , such as a featurette detailing the statistical history of Doctor Who around the time of its fiftieth anniversary . Synopsis . Sarah has begun developing a form of dementia , and she realises that her ability to defend the Earth is diminishing . She must now hand over the task to surer hands . A seemingly suitable replacement , Ruby White , has arrived on Bannerman Road , but can she be trusted ? Plot . Part one . A meteor hurtles towards Earth . Mr Smith redirects it to a safer crash site and says it will contain germ pathogens . The gang hurry to neutralise the germs . The meteorite reads all clear . Then a strange woman appears , claiming to be saving the world . She drives off in a red sports car and Clyde points out that she is doing the same thing as Sarah . Sarah does not look pleased . They find the woman has just moved in across the street and go to find out who she is . She behaves coldly towards them , telling them to get out of her house . Her name is Ruby White and she sees them as amateurs . She moved to Ealing because of all the alien activity — Trueman , the Bubble Shock ! factory , rhinos driving police cars and alien plant life . Sarah decides to stay away from Ruby , but keep her eyes open . The next day , Gita waves to Sarah on her way home . Sarah says she has to make Luke ' s tea and then realises he is at university . Clyde and Rani go to check that she is alright . She calls Luke , just two hours after she last spoke to him . She can ' t remember K9 ' s name . Rani suggests she take a holiday and visit Luke . Mr Smith gives a red alert . A fleet of Dark Horde warriors are heading for Earth . They trace the scan beam and lock onto the attic to neutralise enemy technology . Mr Smith diverts the teleport to an uninhabited area . Sarah gives Clyde a gun and says they must protect the Earth by any means . An advance party of three warriors lands on Earth . Sarah plans to use a device to overload their sensors . She asks Clyde for the sonic lipstick , but he said she told him to bring the gun ( which isn ' t even charged ) . Sarah has made a big mistake . Then Ruby arrives and tosses spheres to Rani and Clyde . She uses an artificial intelligence to convince the Dark Horde that they are faced by a stronger version of themselves . Their logical reaction is to flee . Clyde suggests calling the AI " Mr White " . They take Ruby back to the attic , where Mr White gets along well with Mr Smith . Sarah says she ' d be glad to have an adult friend . Whilst explaining to Ruby how she became involved with aliens , Sarah forgets the Doctor ' s name for a moment , something she can ' t believe she did . She orders Mr Smith to medi - scan her . He tells her there is evidence of brain tissue deterioration . Sarah takes this to mean she is too old to continue defending the Earth . Ruby makes friends with Clyde and Rani , who are eager to show off their knowledge of aliens . Sarah feels very left out . Sarah asks Ruby to take over the duty of protecting the Earth , offering her the house , Mr Smith and Clyde and Rani . Ruby agrees . Sarah goes to leave , not even bothering to tell Luke she is going . She orders Mr Smith to wipe her voice from the command program so she can no longer give him orders . She realises something is wrong and begs Ruby to help her . Instead , Ruby teleports her to a " secret cellar " which houses her stomach . She reveals she is the one making Sarah ill , draining her life force . She is a Qetesh , whose race devours peoples ' thrills and emotions . She targeted Sarah , who has the most exciting life on Earth . Mr White is making a farewell message for Clyde and Rani so they will believe Sarah has gone because " she " will tell them . Ruby ' s stomach drains Sarah directly as Ruby gloats about how she will feast on the Earth . . . Part two . Ruby explains that rather than stop aliens , she will help them and feed on the excitement and terror that humanity will feel . Back in the attic , Clyde and Rani watch Mr White ' s faked video of Sarah . Clyde can ' t believe Sarah has simply gone . He blames Rani for putting the idea of a " holiday " in her head . Mr Smith starts acting strangely . He tries to warn Clyde — " Beware Ruby " . Ruby shuts down Mr Smith and teleports Clyde to her spaceship . It was her prison , until she reprogrammed its game console ( Mr White ) . Ruby leaves Clyde in the prison to suffocate . Rani tries to call Clyde and hears a knock at the door . She opens it to find Luke . K9 , who is back in Oxford , tracks Clyde ' s phone to space . Rani goes to place the phone near Mr White so K9 can reset him and free Mr Smith from his influence , as well as rescue Clyde . Clyde leaves a message on his phone for the others to find , then collapses . Rani distracts Ruby , who is not convinced , but luckily K9 resets Mr White in time . K9 rescues Clyde and the restored Mr Smith imprisons Ruby in a containment vortex , but she escapes . Clyde and Rani go to rescue Sarah . Ruby corners them in the cellar and threatens to devour them completely . Luke arrives and gives Ruby a warning to leave Earth . When she refuses , Mr White sends a hologram so everyone on Earth sees a meteor hurtling straight for them . Ruby cannot handle the sudden inrush of emotions and thrills from six billion people . The stomach swells , then shrinks and releases all the energy it took from Sarah back into her . Sarah sends Ruby back to her prison ship , where Ruby swears to get revenge on her . Sarah thanks her team for saving her , knowing she could count on them while Mr Smith and K9 finally seem to have put aside their animosity after working together to defeat Ruby . Luke takes them all out for a treat and Sarah says that although the universe is full of amazing things , they have stiff competition on Earth . Story notes . Ratings . " to be added " Filming locations . " to be added " Production errors . In Part 2 at around the 24 : 45 mark , you can see the CGI crosses on Mr Smith used to overlay his GUI . Home video releases . " to be added "