The Last Sontaran ( TV story ) The Last Sontaran was the first story of the second series of " The Sarah Jane Adventures " . In it , Maria Jackson left the regular cast , along with her father Alan , who received a job offer in America . He left the decision of moving away up to Maria , who supported him to take the new job . Notably , it acted as a sequel to the " Doctor Who " episode , " The Poison Sky " , dealing with the consequences of the Tenth Doctor ' s battle with the Tenth Sontaran Battle Fleet . This episode featured the last appearance of Chrissie Jackson , who would become directly involved in the alien dealings of Sarah ' s life . Now that her family was leaving for America , she stopped paying visits to Bannerman Road and went back to her life with Ivan . Although Sarah , her friends , and the other Jacksons had been trying to uphold the secret , she finally learned the truth for herself and promised to keep it guarded . Synopsis . Reports of strange lights around the Tycho Project ' s radio telescope lead Sarah , Luke , Clyde and Maria into a terrifying forest encounter . Sarah comes face - to - face with her oldest enemy . Meanwhile , Maria wrestles with a huge decision when her dad is offered a new job in America . Plot . Part 1 . Sarah and Maria discuss the experiences they have shared since Maria ' s arrival in Bannerman Road . They watch the night sky as they look forward to many more discoveries . In rural Goblin ' s Copse , at a radio telescope used in the Tycho Project ' s search for alien life , Lucy Skinner and her astronomer dad , Professor Nicholas Skinner , also watch the night sky . They spot strange lights floating about . Professor Skinner investigates , but goes missing . Lucy investigates , and is promptly captured . The next day , Luke and Clyde play a strategy game with Mr Smith to learn about battle strategies . Sarah interrupts . She had heard reports of the strange lights the previous night . Despite Mr Smith ' s assurances that strange lights rarely herald alien activity , she pursues the story . Maria and Alan have received an important letter , but have found that the implications are far larger than they imagined and will cause an imminent major change in their lives . Alan tells Maria the decision is not just his to make . Sarah , Clyde , Luke and Maria head to the countryside to investigate . They arrive at Goblin ' s Copse and discuss the size of space . They are watched by something . Inside , the team finds Lucy , who tells them that her dad is still missing . Luke and Clyde look outside for the professor after Sarah warns them to stay away from the woods . As the boys search the woods , the creature watching them becomes invisible . While Lucy sleeps , Sarah decides to ask Maria what is troubling her after noticing some unusual behaviour , and Maria reveals that Alan has been offered a job in America , at the head office of his firm . Maria is ambivalent about the news ; she is happy for her dad but sad that she must leave her friends behind . Sarah closes herself off from Maria , telling her she ' s happy for her , but is clearly upset . At his house , Alan discusses the job with Chrissie and how it will change Maria ' s life more than his . In the woods , Clyde and Luke hear a noise . A Sontaran , armed with a gun , reveals himself and chases them . The boys lose him , but come across a cloaked object . When Lucy wakes up , Sarah persuades her to recall the events of the previous night . Professor Skinner appears , though he seems strangely detached and unemotional . He orders Sarah and Maria to leave immediately , which they do . Lucy makes him some coffee and he approaches her strangely . Luke calls Sarah and when she and Maria arrive , he and Clyde show them the object . When the cloaking field is disabled , Sarah Jane immediately recognises the Sontaran ship . Its Sontaran occupant , Commander Kaagh , appears behind them , armed . Maria tricks Kaagh and the group escape , splitting up , with Kaagh chasing them . Sarah Jane and Clyde attempt to reason with Professor Skinner . They find his mind is controlled by the Sontaran . Outside the observatory , Luke and Maria crawl into a vent that leads into the building . Maria and Luke watch from the vent while Kaagh and Sarah talk . He says he was badly wounded when the Tenth Doctor defeated the Sontaran army . As the only survivor of the botched invasion , he has vowed revenge on Earth for his peoples ' humiliation . He reveals his plan to use the Tycho radio telescope to take control of Earth ' s satellites , and steer them to crash into nuclear stockpiles on Earth , triggering nuclear annihilation . Clyde protests , so Kaagh says he will experiment on him . Sarah steps in front of Clyde , defying Kaagh . He pulls out his gun and shoots her . Part 2 . Kaagh shoots Sarah . She sprawls unconscious on the floor . He boasts to Clyde she will be taken to Sontar as a prize and he will be hailed as a hero instead of a laughingstock . Perhaps he will be given a more honourable epithet , like " Kaagh the Avenger " . Luke and Maria , hidden in a nearby vent , watch the scene unfold . They catch Clyde ' s attention and motion for him to join them . Sarah awakens to find she is in a store room with Lucy Skinner . Kaagh has taken her sonic lipstick . Undeterred , Lucy and she start to build a device to jam the satellite . Aware that Kaagh will detect it , they plan to escape when he comes to investigate . Luke , Maria and Clyde provoke Kaagh into chasing them through the observatory ' s corridors and service tunnels . The teens escape into the forest and block Kaagh ' s exit . They run to his shuttle , where Luke uses the chemicals stored there to synthesise a knockout gas to incapacitate the Sontaran . He sets off the intruder alarm . Knowing it will bring Kaagh , Clyde goes to distract him . As Luke works , Maria tells him about the upcoming move which leaves him upset , but Maria reminds him it won ' t matter if Kaagh succeeds . Sarah activates her new invention ; just as she expected , Skinner comes to find it . Sarah and Lucy sneak out , locking Skinner in the room , and try to figure out how to disarm the satellites . They let Clyde in by the same door Luke , Maria and Clyde escaped through earlier , just in time to save him from Kaagh , whom they lock out . Kaagh enters through the main door , breaks down the door to the room Skinner was locked in and rages at him . Maria , uncertain Luke will synthesise the gas in time , decides to ask Mr Smith for more information on defeating Sontarans . As Mr Smith is still in Ealing , she calls her dad and asks him to contact the computer . Alan does so , unaware he has been followed into Sarah ' s attic by his ex - wife , Chrissie . She demands to know what is going on ; Alan quickly brings her up to speed on Sarah Jane ' s alien hunting and Maria ' s role as her assistant . Chrissie realises he is telling the truth because his lip twitches when he is lying . Maria ' s parents , fearful for her safety , decide to join their daughter at Goblin ' s Copse . Sarah , Maria , Clyde , Luke and Lucy all meet up . Sarah takes Luke and Lucy with her to try to deactivate the transmitter , while Maria and Clyde search for the switch that will move the transmitter away from the satellites . However , Kaagh and Skinner get there first and capture them . Luke tries to break into the observatory ' s main computers , succeeding when he realises that Sontarans , who have three fingers on each hand , use base six mathematics . Kaagh appears and reveals Lucy is a sleeper agent . He activates the mind - control chip implanted in her . He orders her to re - activate the transmitter . He threatened Maria ' s life if Sarah tries to stop him . All appears lost , but fate plays an unexpected hand . Chrissie , having been watching from the shadows , bellows " Try my size fives , Humpty " , and swings her high - heeled shoe into his probic vent , knocking him unconscious but electrocuting Chrissie as a side effect . The transmitter is deactivated , this time for good . Kaagh is escorted back to his ship and ordered to return to Sontar , which he is only too glad to do ; he is humiliated that he was defeated by " half - forms " ( children ) and a woman . Sarah is relieved , even if she is not entirely convinced that the Sontaran is gone for good . Six weeks later , Maria and Alan say their goodbyes to Sarah , Luke and Clyde as they leave for their new life in America . As father and daughter pull away , Chrissie whispers to Sarah Jane that she was not " entirely " ignorant of her daughter ' s alien - hunting hobby . The group smiles and waves good - bye to Maria and Alan as they wave back , watching their cab leave Bannerman Road and send the Jacksons on their journey to America . Later that night , Sarah , Luke , and Clyde are looking out at the stars through one of her telescopes . Luke and Clyde tell Sarah Jane they will miss Maria , but Sarah gives them a piece of advice : The trio turn their attention skyward , hoping the best for their friend .