The Thirteenth Stone ( audio story ) The Thirteenth Stone was a made - for - audio " Sarah Jane Adventures " audiobook written by Justin Richards , produced for BBC Audio and read by Elisabeth Sladen . It accompanied the CBBC broadcast of series 1 . Publisher ' s summary . Sarah is helping out on a school trip with Luke , Maria , and Clyde ' s class . On the way home , the group stop off at the Stone Whisperers , a dozen standing stones enclosed by a dome . Set apart from the circle is a thirteenth stone : the King Stone . Legend has it that this is an evil king who was captured in battle by twelve knight s , and turned to stone . To keep him imprisoned , the knights too turned to stone , holding him forever in their power . Nice story , but it ' s just a myth — isn ' t it ? Luke finds himself strangely drawn to the King Stone . Over two metre s high , and covered in moss , it glows with a strange , unearthly light . But when the secret of the stones is finally revealed , the school party ' s enthusiasm turns to terror . Plot . Clyde , Luke and Maria are on a class trip with their teachers Mr Bradbury and Mrs Reiki . Sarah Jane Smith accompanies the class . After visiting the St Margaret ' s House Museum the class is going to the Stone Whisperers , a semi - circle of twelve stones . Set apart from the circle is a thirteenth stone : the King Stone . According to a myth this stone is an ancient warrior king who was captured by the twelve knights that form the circle . Professor Jacqueline Lauton invites the children to see the computer lab , where radar scans of the stones are about to be fully analysed . When this occurs , they see that there are humanoid figures in the centre of the stones , one of whom , Ravage , escapes and takes possession of Luke . The other stones wake up as well . They turn out to be warriors and want to capture Ravage . The warriors had previously imprisoned Ravage and wanted to trap for all eternity inside a stone . They sacrificed themselves , gave up their remaining life - force to keep Ravage in prison . The warriors were arranged to focus their energy on the stone where Ravage was held . After Ravage has escaped all they want is to capture him again . Sarah , Maria and Clyde are afraid that they might hurt the possessed Luke and try to save Luke from the warriors . They also realise that Luke is able to get back the control over himself when they ask him mathematical questions , so they ask him about the complete number of pi and other things . Later they find out that Ravage has possessed Luke because Luke hasn ' t existed for long . Luke has new unformed , impressionable mind . He hasn ' t had a lot of experience and his personality was still forming . So it was easy for Ravage to take over Luke . Sarah tells Luke that she knows that Luke can drive Ravage out of his mind and that she , Maria and Clyde will help Luke . Then Sarah and Maria speak to the warriors they tell them not to hurt Luke because they are sure that he can fight Ravage . The warriors stop fighting Luke . Now Sarah speaks to Luke she tells him that she can ' t do it for him . She adds that she has to let him go and let him be himself , because that ' s what he needs to do . Luke ' s eyes are wide and afraid but then he screams " Get out of me , Ravage ! " . Then Luke says that he is Luke , that he knows who he is and that Ravage can ' t take that away from him . He adds that he has his own life . Then he looks at Maria and Sarah saying he has his own friends and his own mother . Finally , Ravage is defeated , he is expelled from Luke ' s mind and dies . All around Sarah , Maria and Luke the warriors slowly bow their heads . They lower their swords and kneel on one knee as if paying homage to Luke , to the boy who had finally defeated Ravage . Clyde is coming down from the walkway . The kneeling warriors are turning back into stones . Sarah , Maria , Clyde and Luke are standing in the middle of a circle of stones when Professor Jacqueline Lauton arrives . As Prof . Lauton expected a semi - circle of stones and not a circle she is standing there starring , mouth open , then she turns and goes back into the computer room to analys the new data . The main doors are swinging open and Professor Riley and Mr Bradbury arrive . Sarah Jane tells them that nothing special had happened . The thirteenth stone has just lost its inexplicable glow . She adds that the stones have moved because of a Ravage storm , which was a freak magnetic pulse from the thunderclouds coupled with the power surge . Prof . Riley says he has never heard of such a storm . Clyde replies that it is for sure that these stones didn ' t move on their own .