The Eternity Trap ( TV story ) The Eternity Trap was the fourth story in the third series of " The Sarah Jane Adventures " . It saw the return of Professor Rivers , and was essentially a Luke - lite serial . Synopsis . A haunted house , mysterious whispers and secrets in the shadows attract Sarah ' s attention . When Professor Rivers and the gang investigate an old legend , a monstrous creature appears in the night . The terrifying grasp of Erasmus Darkening reaches out from centuries past . Sarah and the gang discover the secrets of Erasmus Darkening , but are they too late ? Ghost s from the past rise up and the quest to find the missing children reaches a climax . It seems that nothing can stop the ancient alchemist ' s rise to victory . Plot . Part 1 . Professor Rivers tells the story of a haunted manor . She speaks of Lord Marchwood and how he employed Erasmus Darkening . Marchwood thought Erasmus could make gold out of nothing . His two children , Elizabeth and Joseph , spy on Erasmus and they vanish for eternity . Rivers is telling the story to Sarah , Clyde , Rani and her assistant Toby . Luke is at home as their standby lest something goes wrong . Sarah Jane separates and finds a book on the history of the manor . She turns from the book case where she is reading , and behind her , the books move . Clyde and Rani go outside and find a shed and a fountain . The fountain ceases flowing and wet footprints appear in the shed . They hear a young girl cry . It stops as Clyde pulls a sheet from a mirror . A man ' s face appears in the mirror . They run back to the manor to find Sarah . Meanwhile in the control room , the camera in the playroom cuts out . Rivers goes to investigate . Abruptly , the nursery monitor starts to play . Seconds later , Rivers vanishes . The gang go to investigate and find all the toys have come alive . On the mirror in the room , a message appears : " Get out " . Clyde and Rani explore and find a secret passageway leading to Erasmus ' lab . Meanwhile Sarah goes outside . She finds a creature with red eyes in the bushes . It advances on her . Lord Marchwood ' s ghost manifests and he fights it off . Clyde and Rani find a computer , then turn around to see Erasmus Darkening . Part 2 . Lord Marchwood arrives with his children to rescue Clyde and Rani . Sarah hears a recording of Professor Rivers saying , " Sarah Jane help me " , over and over . Then she sees her . Rivers warns her , " He is coming for you " , and disappears . Sarah reunites with Clyde and Rani and they find Lord Marchwood . Sarah believes they are not ghosts . Toby , Sarah , Clyde and Rani discover all the people that have disappeared , except for Professor Rivers who hasn ' t been absorbed yet . Erasmus arrives and they all disappear . Erasmus tells them he will come for them all . Sarah and Toby investigate Erasmus ' secret chamber while Rani and Clyde distract Erasmus . Toby tells Sarah of a creature who used to come into his room and watch him every night . Rani and Clyde are chased by something into a game room . When all the games start playing by themselves , they run outside and are locked out . Sarah and Toby find Erasmus ' machine . Sarah suspects Erasmus was trying to get home to another galaxy with the machine . The machine malfunctioned and all the people that disappeared were trapped between dimensions . Clyde and Rani run into the pavilion . Sarah and Toby are interrupted by Erasmus . Sarah works out that the machine is giving Erasmus and all the people that disappeared eternal life . She also works out the creature that attacked her earlier came through the machine . Lord Marchwood again rescues Clyde and Rani . Sarah , Clyde , Rani and Toby reunite with Lord Marchwood . Sarah comes up with a plan to stop Erasmus . Erasmus is destroyed and Professor Rivers is returned . Sarah destroys Erasmus ' machine with her sonic lipstick . Sarah , Clyde and Rani say goodbye to Professor Rivers and Toby . Rani declares that this must be the end of the haunted house dealings . Clyde quickly rebuffs her and says that there were never any ghosts in the first place . He asks Sarah if there really are no such things as ghosts . Sarah answers , " That ' s right . . . No . . such . . thing . . as . . ghosts . " Her voice slows and becomes hesitant as she peers up at the manor , seeing something peculiar from up above , before slinking into her car . As the trio drive away , Lord Marchwood and his children watch from the window .