Changing Time Changing Time was a 2 | entertain DVD documentary about the making of the " Doctor Who " serial " The Hand of Fear " . As it was Sarah Jane Smith ' s final classic story , it also looked at her relationship with the Doctor . It was divided into chapters . Each covered a subject . Prologue - Beginnings . Glyn Houston and Rex Robinson explained how they became actors . After leaving the army , Houston took up acting and got leading roles because famous actors did not want to do television . Bob Baker told of how he was approached by Dave Martin , who requested they write a story together . Elisabeth Sladen recounted her pre - " Doctor Who " career . Colin Mapson was on an attachment to " Doctor Who " as a visual effects designer for nine months before he was contracted to begin work . Casting Sarah Jane . An interview was required for candidates auditioning for the part of Sarah Jane . Barry Letts conducted the interviews and asked anyone back who he thought would be a good contender for the part . Auditions for the part took place in Threshold House , Shepherds Bush . Elisabeth Sladen attended after being called back . They were required to perform a scene specially written by Letts . Stephen Thorne performer opposite each candidate . Letts was impressed by Sladen ' s ability to portray both fear and bravery at the same time . After Sladen ' s aution , Jon Pertwee greeted her and signalled his approval to Letts ' decision to give her the part . Changing Doctors . Pertwee was open to Sladen about his decision to leave . During the filming of " Planet of the Spiders " , Pertwee distanced himself from the other . Sladen suggested he didn ' t want to not be the Doctor any more . Letts announced that he was looking for a new Doctor . Bill Slater suggested Tom Baker as the two had worked together before " Who " . At the time , Baker was finding it hard to get work and so was deeply worried . It was at this time that he got the part of the Fourth Doctor . Sladen explained the awkwardness of the regeneration scene and Baker also voiced his thoughts on the transition . Baker recalled how he would tease Pertwee by pretending he had turned down large sums of money . Playing the Doctor . Terrance Dicks explained how he emphasised the Doctor ' s eccentricity . Philip Hinchcliffe told of how his role as a " Doctor Who " producer was instantly recognisable due to the show being very well known . A Special Relationship . Baker and Sladen were friendly in studio but only met once outside during their time on " Who " . After leaving the show they remained friends . Sladen commented on how little Baker had changed since working on the show . The Hand of Fear . Douglas Camfield approached Hinchcliffe with a story in which the Doctor met the Foreign Legion . Sarah Jane was to die at the end but Hinchcliffe was not happy with the story and so it was not commissioned . Sladen left at a time she believed her character to be popular . She wanted to leave people wanting more , rather than boring them . " The Hand of Fear " , a script already in existence , was chosen for Sladen ' s swansong . Sladen did not want to be married or killed off . On Location . A look at the setting of " The Hand of Fear " . was used for location filming . The cast recall their experiences and filming on set . In Studio . Baker and Sladen commented on the performance of Glyn Houston , in particular how he made his character ( Watson ) interesting . Mapson explained his worries as to making the hand move . He told of how colour separation overlay was used to create the effect . Breaking Apart . Sladen gave her thoughts on Sarah ' s final scene . She wasn ' t happy with it and guessed the writers did not want it to be too sloppy . Baker explained how he portrayed the Doctor in the same scene . Epilogue - Endings . Lennie Mayne did the whistling for Sarah Jane as she walks away at the end . Sladen herself could not whistle .