Sarah Jane Smith managed to gain access to a UNIT base by posing as her aunt who was a renowned virologist, but her adventure really began when she accidentally stowed away aboard the Tardis just as the Doctor traveled back to the Middle Ages in search of scientists abducted by a Sontaran soldier named Linx to repair his ship. Sarah Jane initially believed that the Doctor was responsible for the kidnappings, and in league with a medieval bandit named Irongron. In reality, Linx was supplying Irongron's forces with rifles. Sarah Jane soon realized her error, and with the Doctor, helped to defeat the Sontaran and return to the present where she would remain in his company as his new companion.
She would travel with the Third Doctor seeing many things including a dinosaur invasion, encountering the Daleks on her first journey off world and eventually being present with the Brigadier as the Third Doctor regenerated after his body was devastated by radiation from the crystals of Metebelis III. With the Fourth
Doctor’s arrival Sarah Jane would continue to travel the universe with him and would be present for one of the most defining moments in all of time, the creation of the Daleks by Davros on Skaro. Eventually Sarah Jane would leave the Doctor after he is summoned back to Gallifrey, which at the time had a strict policy against the presence of off-worlders, it would be later reviled that the Doctor left Sarah Jane in Aberdeen not South Croydon as he had thought.
Sarah Jane would continue to uncover the presence of alien menaces back on earth, the Doctor even sent her K9 Mark III as a companion. It would be K9 that would attempt to warn Sarah of the imminent danger of a Time Scoop that would whisk her away to Gallifrey itself to be a part of the game of Rassilon along with many other of the pervious Doctors and there companions, it would be here that she would be reunited with the Third Doctor, the Brigadier and meet the Fifth Doctor. Eventually K9 would break down and Sarah had lost what little
connected her to the Doctor but would continue with her investigative journalism, moving from South Croydon to Ealing Sarah would seek out stories that were more than they seemed. Once such case was a school with unnaturally high results, upon a personal visit Sarah Jane would encounter a strange teacher called ‘John Smith’ who would later be reviled to be non other than the Doctor only now in his Tenth incarnation. Together with the Doctor, his companion Rose and her boyfriend Mickey Smith they would defeat the Krillitanes but loose the reactivated K9.
As the Doctor was about to depart Sarah is offered the chance to rejoin the Tardis crew by Rose, but she declined stating that she now had a life of her own. After another farewell to the Doctor the Tardis dematerializes to reveal a brand new K9 ready to accompany Sarah Jane on her new adventures. Sarah Jane now chose to stand as a protector of earth but would use methods less hostile as U.N.I.T and Torchwood. With the aid of an extraterrestrial supercomputer code named ‘Mr. Smith’ Sarah Jane would do battle with many threats on her own until the rescue of an artificial human boy who she would adopt as her own son, Luke Smith. Together with Luke and some of his friends Sarah Jane and her new team would fight back attacks from Slitheen, Ban and on several occasions her old foes the Sontarans.
When the earth was stolen Sarah Jane would become one of the Children of Time and and help fight back Davros whom she had thought died back on
Skaro many years before, Mr. Smith and Luke were crucial to returning earth back to its original location after the defeat of the Daleks. Sarah Jane would encounter the Doctor once more as he would return to save her from a wedding arranged by the Trickster that would have resulted in her loosing all memory of the countless times she had saved the earth and the constant danger it faces. With the Tricksters defeat would come another goodbye, but she would see the Tenth Doctor one final time after he saved her sons life, he would wave goodbye to his old companion signaling his incoming death and regeneration. Sarah Jane Smith would continue the fight in the honor of the Doctor with her son and friends from her Attic in Ealing.
A year later, she encountered the eleventh incarnation of the Doctor, and Jo Grant, another former companion of the Third Doctor. By this time, Luke had left to go to Oxford University.
Sadly, Elisabeth Sladen, the actress who portrayed Sarah Jane Smith, passed away.