Sarah Jane Smith is an investigative journalist trying to infiltrate a top secret research facility when she meets the Doctor, who just so happens to be the scientific adviser at that UNIT facility. Her investigation leads her to sneak aboard the TARDIS, and she soon finds herself in the middle ages helping the Doctor fend off a Sontaran soldier.

Sarah Jane continues traveling with the Doctor on several more adventures, and is present when the Doctor falls victim to a poison that his body can't fight and is forced to regenerate for the third time.

This new version of the Doctor seems quite strange, but Sarah Jane is still willing to continue with him on his travels. However, the Brigadier has assigned Harry Sullivan, a navy surgeon, to look after the Doctor, and he is soon dragged into traveling through time and space with the pair.

After many more adventures, the Doctor abruptly returns Sarah Jane to earth when he receives a summons from Gallifrey. Sarah feels a little miffed that the Doctor so easily leaves her standing in the street with her suitcase, and not even on the right street to boot.

It will be many years and regenerations before Sarah Jane runs into the Doctor again during School Reunion. She just so happens to be investigating the same school that has also caught the Doctor's attention. She is older now, but over the years has still done her best to protect the earth.

By the time Sarah Jane is done helping the Doctor defeat the Daleks in The Stolen Earth and Journey's End, she has been joined by her own gang of young adventurers. The group does their best to handle a variety of alien menaces right in their own backyard.

Sarah Jane encounters the Doctor a few more times over the years and also meets her predecessor Jo Grant during Death of the Doctor.