The Empty Planet ( TV story ) The Empty Planet was the fourth story in the fourth series of " The Sarah Jane Adventures " . It was notable for its minimal cast and its exceptionally heavy use of location filming . The story focussed on Clyde and Rani , including at least one of the characters in nearly every scene . The events of this story also strengthened their personal connection , hinting at a possible romantic attraction . Synopsis . Clyde and Rani are apparently the only survivors of the human race . The whole of Earth is empty – even Sarah has vanished . A deserted London holds terrors of its own , mainly in the form of two mysterious and menacing robots . Plot . Part 1 . Sarah tells Mr Smith to do a maximum scan . Clyde asks what is going on . Rani tells him that Mr Smith picked up an alien energy trace for a second , then it vanished into the signals of every energy source on Earth . When they leave Sarah ' s house , Rani reminds Clyde of their school assignment . Clyde sees no point in doing the reading considering they might be invaded . Rani ' s dad comes to see her in her room , but she asks him to leave so she can finish the assignment . Clyde ' s mum also comes to see him . She compliments him on his latest cartoon drawings . As they sleep , the mix of signals and sounds transmitted across Earth is suddenly cut out . Rani wakes to find her parents missing . She sees no - one on the street . Sarah is also gone and Mr Smith does not seem to be in the computer that houses him . Rani searches for another person . She finds nothing has a signal any more . She prays she is not alone . She hears a knock at the door and opens it to find Clyde . They head into town to look for someone besides them . They can ' t find anyone and realise that if everyone suddenly disappeared , there should be crashed vehicles everywhere . There are not , which means that whatever took the humans didn ' t want to do any damage . They go to a cafe for breakfast and try to figure out why they have not been taken . They decide to return to the attic , but notice crates being knocked over . They spot another person , who runs away . Giving chase , they follow him to an apartment block . He is a schoolboy called Gavin who has been living with his aunt and uncle since his mother died , his father having disappeared . Rather than being relieved to see other people , Gavin is afraid of Rani and Clyde . They try to convince him they mean no harm and Rani tells him about aliens to try to gain his trust . Gavin is sceptical . As they try to persuade him to help , a strange noise is heard . Gavin slips away while Rani and Clyde try to work out what it was . Clyde points out a couple of strange facts about Gavin . . . he should have been happy to see other people on Earth rather than afraid . Also , his room is almost bare and there are no pictures of him with his aunt and uncle indicating they care little for him . They go back to the cafe and see a strange image on all the screens , even the mobile phones . They hear a noise getting closer and investigate . Rani notices Gavin and goes down an alley ; Clyde looks around the corner and sees a yellow robot . It corners him whilst Rani is cornered by a red robot . The robots both lift their arms and point them directly at Rani and Clyde . . . Part 2 . Gavin pushes the robot facing Rani against the wall so they can escape . Clyde runs away from the yellow robot and hides in a store . He evades it and meets up with Rani and Gavin . They look at the images on the screens and go in search of the robots , then decide to return to the cafe . Rani and Clyde talk about what makes them different , mentioning time fissure s , space travel and the TARDIS , much to Gavin ' s confusion . All of these things pertain to Sarah as well , however . Clyde then remembers something that connects only him and Rani . . . during their encounter with the Judoon , the two were given a ticket forbidding them from leaving Earth ; hence it would be illegal to remove them , which is the only logical explanation why the robots left them behind . This doesn ' t explain why Gavin is still there ; he knows nothing about aliens . The robots burst into the cafe . The three children escape out the back door . Rani and Clyde tell Gavin to get away , thinking the robots must be after only them . The two split up to distract the robots . They are each cornered again . The robots scan them , but do not kill them . In the cafe , Clyde shows the robots a newspaper so they can learn the language quickly . The robots reveal that the strange image is a countdown . They demand the " sun and air " , saying that if it is not given to them by the end of the countdown , the human race will not return . Clyde and Rani are confused by the robots ' demand , but then Rani realises that they aren ' t saying " sun and air " , but " son and heir " . It turns out that Gavin ' s dad was an alien king . He has died , and the robots have come to take Gavin to their planet . They sent the news in the energy trace from the previous night , but Gavin never received it . Clyde and Rani search for Gavin , finally locating him at the Ealing Circle Nature Reserve . The robots cannot see him . They determine that Gavin is wearing a bio - damper ring to shield his alien half ; when this is removed , the robots send him the information again , showing him the planet he is meant to rule . Gavin agrees to go . He orders the robots to return everyone to Earth . He bestows upon his new friends the titles Lord Clyde and Lady Rani before he leaves , and gives his bio - damper ring to Rani . Everyone returns to their rightful places . Mr Smith fixes the records to indicate that Gavin has moved to Australia . Clyde and Rani think about the fact that if they had never met Sarah , they would have been in big trouble . Sarah worries that one day , if their adventures together come to an end , she doesn ' t want the two of them to be alone like she was . Rani shoots down her fears by saying after the day ' s events , she has no idea what it is like to be alone . Sarah sees she has a fair point and decides to reward her friends by ordering a pizza , for saving the world . After she leaves , Clyde and Rani agree that they are not alone , because they ' ve got each other . She gives him a warm smile and hands over Gavin ' s ring so he may wear it like she has , a slightly more intimate gesture . They affectionately address each other by their knightly titles and share a high - five , a score one for the " hangers - on " of Sarah ' s troupe , who have proven they are indeed quite the opposite — invaluable protectors of the Earth . Story notes . Ratings . " to be added " Filming locations . 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