Warning: Spoilers ahead for Doctor Who season 14, episode 3, "Boom."

Summary

• Susan Twist's role in Doctor Who's "Boom" marks a significant shift in her character interaction with the Doctor and Ruby.
• Despite previously playing various characters, Twist's face is first seen directly in "Boom," leading to questions about her ongoing role.
• The Doctor not recognizing Twist's character in "Boom" reveals new clues about her mysterious identity.

Susan Twist's guest appearance in Doctor Who season 14, episode 3, "Boom," differs from her previous cameos in a way that should alter her future presence in the show. "Boom" marks Twist's fourth Doctor Who appearance, all of which have come in the Disney era of the show. However, she seemingly doesn't have a consistent character in the Doctor Who season 14 cast. Each role the actress has played on the show has been credited differently, but her "Boom" character interacts with the Doctor in a way that's so different from her previous appearances that it's impossible to ignore.

Twist appeared early in Doctor Who's Disney era, playing Mrs. Merridrew during the Isaac Newton scene in "Wild Blue Yonder." Although she didn't appear in the final episode of the Doctor Who 60th-anniversary specials, she did return as a new character in the 2023 Christmas special, "The Church on Ruby Road." Since then, she has become increasingly present in Doctor Who, with the mystery of her ever-changing personas raising questions about her role in the underlying mystery.

The Doctor & Ruby Actually See Susan Twist's Face In Season 14's "Boom"

Susan Twist plays the Ambulance AI

"Boom" marks the first time that Ruby and the Doctor directly lay eyes on a Susan Twist character. Prior to this episode, the Doctor and his companion have always been looking the other way or been in a situation where Twist's character is obscured. For example, Twist is in the crowd at Ruby's gig in "The Chuch on Ruby Road." In addition, Ruby and the Doctor look away from the screen when the recording of Gina Scalzi (played by Susan Twist) is being played in Doctor Who season 14, episode 1, "Space Babies." Similar instances have happened during her other previous cameos.

Although Susan Twist doesn't physically appear in "Boom," she voices the Villengard Ambulance AI, as well as the machine's screen displaying her likeness. Ruby and the Doctor both have extended interactions with the Ambulance and therefore see and hear Susan Twist. They have both heard her before, but "Boom" is the first time they've seen her. So, in future encounters with Doctor Who characters played by Susan Twist, Ruby and the Doctor are much more likely to look upon her with a sense of familiarity.

"Boom" Reveals An Important Clue About Susan Twist's Mystery Doctor Who Character

It seems that the Doctor doesn't know Susan Twist's character

Susan Twist failing to be spotted in all previous encounters with the Doctor suggested that she is someone the Time Lord could recognize. Now that he has seen her, that doesn't seem to be the case. However, the fact that "Boom" is the first time the Doctor sees Twist's face means it's been impossible for him to spot the trend emerging. Now that the Doctor knows what Susan Twist's face looks like, it's far more likely that he will be aware of her inevitable and ongoing returns during Doctor Who season 14.