This article contains spoilers for Doctor Who: The Legend of Ruby Sunday


The mystery of actor Susan Twist's recurring appearances on Doctor Who was finally resolved in this week's episode.

The Legend of Ruby Sunday revealed the true identity of Twist's character, who has popped up in various guises since 2023 episode Wild Blue Yonder – without explanation, until now.

This week, we saw the Doctor (Ncuti Gatwa) seeking the help of his allies at UNIT HQ in identifying Twist's character, who has appeared variously as Isaac Newton's maid, a gig-goer watching Ruby (Millie Gibson)'s band, a comms officer on the planet Pacifico Del Rio, a tea lady in 1960s London, the AI representation of an advanced ambulance, a hiker in 21st century Wales, the mother of Lindy Pepper-Bean (Callie Cooke), and the mother of a Duke in the Regency era.

Her latest alter-ego was Susan Triad, a tech genius and entrepreneur set to deliver a broadcast message to the nation, announcing the free release of her firm S Triad Technology's latest software.

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Susan Twist as Susan Triad in Doctor Who
Susan Twist as Susan Triad in Doctor Who BBC

UNIT has been monitoring Triad – not just because she's a high-flying businesswoman who they suspect might have got her hands on extraterrestrial gadgetry, but because "S Triad" is (obviously!) an anagram of TARDIS, further piquing their interest.

The Doctor initially suspects that Triad might be his granddaughter Susan, regenerated since their last encounter and using the TARDIS acronym as a means of sending a message – but this transpires not to be the case...

Arriving at Triad HQ, the Time Lord realises that, though she's explained them away as just "bad dreams", Susan Triad has vague recollections of each of their previous encounters – she is indeed one being appearing throughout time and space in different forms, rather than different people who all share the same appearance.

But how? The answer lies in a previous episode, The Devil's Chord, where the arrival of Maestro (played by Jinkx Monsoon) was preceded by an appearance from one "Henry Arbinger", apparently an innocent schoolboy but in fact a harbinger for the God of Music – H-Arbinger... geddit?

Ncuti Gatwa as The Doctor, Bonnie Langford as Mel and Susan Twist as Susan Triad in Doctor Who. The Doctor is shaking Susan's hand.
Ncuti Gatwa as The Doctor, Bonnie Langford as Mel and Susan Twist as Susan Triad in Doctor Who James Pardon/Bad Wolf/BBC Studios

The Legend of Ruby Sunday reveals that UNIT officer Harriet (Genesis Lynea) is another such harbinger – full name Harriet Arbinger – and that the character played by Susan Twist, is likewise, a herald of Sutekh, a God-like being of enormous power and an old foe of the Doctor's.

(There's another pun in there – S Triad Technologies... Sue Tech... Sutekh.)

Transformed into a monstrous creature that can turn people to ash with a touch, Susan mocks the Doctor for believing she might be his long-lost granddaughter. "Did you think I was family, Doctor?" she says. "I bring Sutekh’s gift of death for you and for all your tiny, vile, incessant universe."

So there we have it – the mystery solved... and you can learn more about Sutekh and his history with the Doctor here.

Now we just need to uncover the true identity of Ruby Sunday's mother and we'll finally be able to get some sleep...

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Doctor Who continues on Saturday 22nd June on BBC iPlayer and BBC One. Previous seasons are available to stream on BBC iPlayer.


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