Warning: spoilers ahead for Doctor Who season 14, episode 3, “Boom.”
Doctor Who season 15 faces a dilemma as a new companion is set to join the Doctor and Ruby as a permanent member of the TARDIS. It’s Ncuti Gatwa and Millie Gibson leading the Doctor Who cast in season 14, but the dynamic duo will become a tenacious trio soon enough. Despite widespread reports that Gibson would not continue as a full-time companion, an official announcement later confirmed Doctor Who season 15 will partner the Doctor and Ruby with an as-yet-unnamed companion played by Andor actor Varada Sethu.
Complicating matters further, Sethu makes her Doctor Who debut early, portraying Mundy Flynn in season 14, episode 3, “Boom.” The story’s final scene gives no indication that Mundy aspires to join the TARDIS crew, and while the Doctor may circle back to Kastarion 3 and pick her up before season 15 kicks off, Doctor Who history suggests Sethu’s season 15 character will be someone entirely new. Freema Agyeman, Karen Gillan, and Peter Capaldi all featured in guest roles before becoming full-time Doctor Who cast members.
Assuming Varada Sethu returns in season 15 as a fresh character, Doctor Who cannot sweep the obvious resemblance to Mundy Flynn under the narrative rug. Not only do the Doctor and Ruby both spend plenty of time with Mundy in “Boom,” the soldier’s face remains on full display at all times. If the Doctor can calculate an object’s precise weight merely by seeing Ruby throw it into the air one time, then he can remember a soldier’s face.
More importantly, only five episodes of Doctor Who season 14 are left, followed by a Christmas special, before season 15 presumably airs in 2025. In all likelihood, therefore, only six episodes will pass between the Doctor meeting Mundy Flynn and the Doctor taking Varada Sethu’s new character as his companion. Given this perilously short gap, ignoring the visual similarity between characters simply isn’t an option. For neither the Doctor nor Ruby to bring up their new friend’s obvious resemblance to the Anglican Marine they encountered on Kastarion 3 would be ridiculous.
Doctor Who could perhaps get away with ignoring the déjà vu if Sethu’s two characters met different Doctors. Karen Gillan, for example, first appeared – in heavy makeup, it should be noted – during David Tennent’s stint as the Tenth Doctor, then resurfaced as Amy Pond for Matt Smith’s tenure. Gillian’s two characters appearing in different eras of Doctor Who reduced the need to explain why her Soothsayer looked a bit like Amy Pond, but with Varada Sethu returning only six episodes later and both of her characters meeting the same Doctor, season 15 won’t have that luxury.
Past Doctor Who seasons set a precedent for explaining instances of multiple characters sharing the same actor. Freema Agyeman initially appeared as a Torchwood employee in Doctor Who season 2 before being cast as Martha in season 3, and this plot hole was quickly addressed via the suggestion that Agyeman’s two characters were cousins. Peter Capaldi’s dual role as the Twelfth Doctor and Caecilius became a fully-fledged plot point, culminating in the Doctor realizing he had subconsciously taken Caecilius’s form to remind himself of the lessons learned during that particular adventure.
Doctor Who season 15 can, and should, continue in that vein by providing an in-universe reason for Varada Sethu’s return. Assuming the Doctor reverts to type and recruits his next companion from present-day Earth, the most logical explanation would be making Sethu’s season 15 companion character an ancient ancestor of Mundy Flynn. The Doctor and Ruby might even accept this stranger as an extra TARDIS passenger partly because of her biological connection to someone they already befriended in the past (or, indeed, the future).
Although the British sci-fi franchise does have a history of promoting guest stars to main roles and then explaining why those characters look alike, Doctor Who also has a history of introducing new companions early as part of ongoing storylines. Jenna Coleman was confirmed as Matt Smith’s new companion in 2012, but shockingly debuted in “Asylum of the Daleks” while Amy Pond was still on the show. Coleman’s surprise cameo set up Doctor Who‘s “Impossible Girl” arc, in which the Eleventh Doctor became preoccupied with the various versions of Clara floating around his timeline.
A similarly lore-heavy explanation could be behind Varada Sethu’s curious turn in “Boom” – and one Doctor Who season 14 mystery supports that idea. Since the 60th anniversary episode “Wild Blue Yonder,” actor Susan Twist has made cameos as various minor characters: Mrs. Merridew, an audience member at Ruby’s gig, Gina Scalzi, a 1960s tea lady, and the Ambulance’s avatar. Something is evidently afoot, with one person taking on numerous guises across time and space.
The Susan Twist situation might translate to Varada Sethu. Whatever reason hides behind Susan Twist playing various characters in Doctor Who season 14 could also be behind Varada Sethu playing both Mundy Flynn and season 15’s companion-in-waiting.