Warning: spoilers ahead for Doctor Who's "Joy to the World."

Ruby Sunday's brief return to Doctor Who season 15.

Sure enough, Doctor Who season 14 ended with Ruby exiting the TARDIS after reuniting with her long-lost mother. 2024's Christmas special, "Joy to the World," finds the Fifteenth Doctor operating alone, solemnly preoccupied with thoughts of Ruby - making two drinks instead of one, staring longingly at the telephone, etc. - throughout the episode. Curiously, Millie Gibson does make a brief cameo in "Joy to the World," looking wistfully out of a window before receiving a phone call from her mother. Fleeting though it is, Ruby's scene gives an indication of her role in Doctor Who season 15.

What Doctor Who Has Already Revealed About Ruby Sunday's Future

Ruby's Involvement Has Been A Topic Of Speculation

Millie Gibson's involvement as a Varada Sethu ing as a companion for season 15 were accurate, but stressed the newcomer would be a third addition to the existing duo of Gatwa and Gibson, not a direct replacement for Ruby. The press release stated, "He [the Doctor] will have two companions by his side as Varada Sethu steps aboard the TARDIS," which made it sound like Sethu would simply the current TARDIS crew to create a full-time trio.

Ruby's decision to leave the Doctor at the end of Doctor Who season 14, however, suggested otherwise by putting a fairly definitive stop to her time travelling. Millie Gibson will definitely feature in Doctor Who season 15, then, the extent of her presence, and whether she will be a permanent companion, is murky.

Based on season 14's ending and RTD's comments, it's possible that Ruby will have a reduced role moving forward. Sethu could occupy the main companion position and appear week-in-week-out, while Ruby will become more like a Captain Jack or Rory Williams figure, ing the fun now and again. On the other hand, enough time could in-universe for Ruby to feel ready to re the TARDIS in season 15's first episode, and Doctor Who will return to the classic two-companion dynamic seen previously with Nessa and Tegan during the Fifth Doctor's era.

Ruby Sunday's New Doctor Who Cameo Suggests Her Companion Days Are Over

Ruby Is A Retired Hero In Doctor Who Season 15?

Ruby Sunday's cameo in the 2024 Doctor Who Christmas special provides further evidence that Millie Gibson will have a part-time schedule in season 15. While Ncuti Gatwa's Fifteenth Doctor spends much of "Joy to the World" wishing he could phone Ruby, the biggest takeaway is that he never actually does so. If Doctor Who planned to bring Ruby straight back to the TARDIS in season 15's premiere, it would make sense to reestablish by having the Doctor call Ruby in the Christmas special, even just to say "merry Christmas!" That way, Ruby's comeback would feel less like a jarring U-turn after her season 14 exit.

As the Doctor begins peeling back the truth about Ruby's enigmatic neighbor, Ruby herself will find it impossible not to get involved.

Instead, "Joy to the World" gives the impression that Ruby has truly moved on from the Doctor. By showing Ruby receiving a call from her mother, Doctor Who implies that Fifteen's former companion is content with her current situation, happily moving forward, and doing exactly what she said she would upon quitting the TARDIS: making up for lost time with her family. Ruby exudes fulfillment in her Christmas 2024 scene, ing her times with the Doctor fondly but not at all rueful that she walked away.

It seems improbable, therefore, that Ruby will contradict herself in Doctor Who season 15 by ing the Doctor and his new friend as a power trio. More likely, Ruby will be inadvertently drawn into situations the Doctor is already involved in. The question of her mother's identity might be solved, but Doctor Who's Mrs. Flood mystery is still ongoing, and as the Doctor begins peeling back the truth about Ruby's enigmatic neighbor, Ruby herself will find it impossible not to get involved.

Doctor Who's 2024 Christmas Special Hints Ruby Sunday's Story Isn't Over

Doctor Who Clearly Isn't Done With Ruby, Even If She's Stepping Back

Ruby Sunday's chances of being a mainstay in Doctor Who season 15 are fading rapidly, but one must consider how significant it is that Millie Gibson gets a cameo in "Joy to the World" at all. If Doctor Who secretly wanted to leave Ruby in the past and move onto Fifteen's next companion, it would be very easy to simply not show Ruby in 2024's Christmas special at all. Taking the complete opposite approach, "Joy to the World" goes to the trouble of including Ruby, despite her scene having no impact whatsoever on the Christmas episode's plot.

The sole purpose of Gibson's cameo is to remind audiences that Ruby still has a part to play in coming events. Indeed, Ruby's yuletide return will be rendered completely pointless if Doctor Who season 15 does not have something substantial in the pipeline for Fifteen's first companion. Even if Ruby only gets a handful of episodes, the way "Joy to the World" keeps Gibson's character in focus must mean her story is a big one, whether that be revealing the truth about Mrs. Flood or something else entirely.

What Ruby Sunday's Role In Doctor Who Season 15 Could Be

There's A Flood Coming...

Mrs. Flood is undoubtedly powerful and possesses a vast wealth of cosmic knowledge, but her true nature is still obscured after Doctor Who season 14. Nevertheless, Anita Dobson's character knows all about the Doctor, and even had advanced awareness that the One Who Waits was secretly Sutekh. Flood typically only reveals her ominous, fourth wall-breaking self when no other character is looking, but the facade slipped shortly before Sutekh's death wave, and Mrs. Flood's sinister persona sneaked out in front of Ruby Sunday's grandmother, Cherry.

She may no longer be following the Doctor from disaster to disaster each week, but Ruby's arc only feels two thirds of the way complete.

Consequently, Cherry Sunday is the only Doctor Who character with any kind of inkling that Mrs. Flood is more than a harmless neighbor. If Ruby finds out what her grandmother knows, the Doctor will naturally be her first phone call, which could explain how she winds up riding the TARDIS again in season 15. The connection to Mrs. Flood could even go deeper, and there might be a more elaborate reason she specifically chose Ruby as a neighbor. If the Doctor figures out that reason, he might then be compelled to protect Ruby from the danger Mrs. Flood poses.

Away from Mrs. Flood, there are still plenty of ways Ruby Sunday could become pivotal in Doctor Who season 15. Ruby Sunday's father could be a person of significance, for example. Alternatively, Ruby's hidden knowledge of future events concerning Roger ap Gwilliam could come into play, and "73 Yards" also never revealed what the older Ruby said that made everyone scared of the present-day Ruby. With so much ambiguity still following Ruby, any one of these details could be a reason for her to reunite with the Doctor.

Doctor Who season 15 does not currently have a release date, but May 2025 looks likely, according to Russell T Davies (via TheBigIssue).

Modern Doctor Who has also set a precedent for companions returning. Rose came back to warn the Doctor about a new threat, Martha chose to continue fighting evil by ing Doctor Who's UNIT organization, and Donna was drawn back to the Doctor by unfinished business.

Ruby Sunday could take any of those same routes back to the TARDIS - warning the Doctor about Mrs. Flood, helping UNIT after meeting Kate Stewart in Doctor Who season 14, or being pulled back by the unsolved mysteries of "73 Yards." She may no longer be following the Doctor from disaster to disaster each week, but Ruby's arc only feels two thirds of the way complete heading into her second season.

Sources: TheBigIssue