Warning: contains spoilers for recent episodes of Doctor Who!

Doctor always travels with companions, who help keep him grounded in reality. He has traversed the universe with numerous companions. In recent episodes, the Doctor has become obsessed with finding his granddaughter Susan, and 2009’s Doctor Who: The Forgotten #6 provides context as to why.

Doctor Who: The Forgotten #6, first published by IDW, was written by Tony Lee and drawn by Kelly Yates. Throughout the issue, the Doctor has shared an adventure with a shape-shifter, who takes the form of previous companions, such as Leela, Adric and Mel. Finally, the alien transforms into a vision of Susan. Seeing her visibly upsets the Doctor, who explains he only left her behind because she was young and in love, and needed to find her own destiny.

The Doctor laments, however, that Susan was taken from him before he could return.

Companions Are Integral to the Doctor Who Mythos

The Doctor's Very First Companions Included His Granddaughter Susan

The multitude of companions the Doctor has traveled with over the years serve a variety of functions. During the classic era of Doctor Who, from 1963-1989, the companions were “stand-ins” for the audience, asking expository questions about whatever threat they were up against. Very rarely does a classic companion get their own story arc. Still, the actors were able to make these characters some of the most memorable in pop culture. When Doctor Who returned in 2005, the companions’ stories became far more integral to the show, and in some instances eclipsed the Doctor’s.

The companions of the First Doctor came from all over space and time. His very first companions were Ian Chesterson and Barbara Wright. Ian and Barbara were introduced to the canon as teachers of the Doctor’s granddaughter Susan, played by Carole Ann Ford. The pair wanted to meet with Susan’s caretaker, putting them into the Doctor’s path. In the first serial, titled “An Unearthly Child,” which first aired in 1963, the two teachers, Susan and the Doctor, took the TARDIS back to prehistoric Earth, thus launching one of the greatest voyages in pop culture history.

The Doctor's Companions Come and Go, But Susan Was Different

Was Susan Wiped Out in One of the Time Lord Purges?

One of the harshest realities of the Doctor’s life is that his companions will eventually leave him, and Susan’s departure was especially bittersweet. In “The Dalek Invasion of Earth,” first airing in 1964, Susan met a young man on an apocalyptic Earth, and fell in love. Sensing that Susan was anxious to start her own life, the Doctor left her behind, imploring her to “go forward in all her beliefs.” The Doctor also promised he would one day return, but he never did, at least on-screen. Visions of Susan would appear in specials, such as 1983’s The Five Doctors.

In the most recent season of Doctor Who, the Doctor has become increasingly obsessed with finding Susan. The Fifteenth Doctor believed the enigmatic Susan Triad was the regeneration of his granddaughter, but this was not the case. In “The Interstellar Song Contest,” Susan (played by Carole Ann Ford) comes to the Doctor in a vision, begging him to come find her. In “Wish World,” Susan appears again. Doctor Who’s current season has one more episode left to air, which may finally establish Susan’s status in canon, especially after the Time Lords were wiped out during the Fourteenth Doctor’s reign.

Will the Doctor Be Reunited With His Granddaughter Susan?

The Doctor and Susan Have Issues To Work Out

Doctor Who has left it vague why he has become so obsessed with finding Susan, but The Forgotten #6 sheds some light on the subject. When the Doctor left Susan on 22nd century Earth, he promised her he would come back for her. Yet, life happened, and the Doctor, as far as fans know, never returned. The Forgotten #6 also leaves Susan’s final fate vague, and the Doctor’s comments towards the alien resembling her almost imply she was killed during the Last Great Time War. The show itself never clarified if she indeed died in that conflict.

Doctor Who: The Forgotten #6 makes it clear the Time Lord carries a great deal of guilt over his perceived abandonment of Susan.

Doctor Who: The Forgotten #6 makes it clear the Time Lord carries a great deal of guilt over his perceived abandonment of Susan. While the Doctor cared deeply for all his companions, Susan was different: she was family. The Doctor accepts that his companions will one day leave him, but in Susan’s case, he leaves her behind. Why he did not go back for her was never revealed, making Susan one of Doctor Who’s biggest dangling plot lines. Susan’s return almost seems guaranteed at this point, and it promises to be bittersweet.