The Doctor (Ncuti Gatwa) turns up at UNIT HQ and meets with Kate Lethbridge-Stewart (Jemma Redgrave) and her team. UNIT has identified the mysterious woman that keeps popping up in the Doctor’s adventures as Susan Triad (Susan Twist), the head of S Triad Technology. S Triad is an anagram of TARDIS and it is thought to be some kind of trap. The Doctor thinks that Susan Triad may be his granddaughter, Susan Foreman. Ruby (Millie Gibson) leaves with Rose Noble (Yasmin Finney), the daughter of former companion Donna Noble, now working for UNIT. They have a VHS tape of security footage from the night the newborn Ruby was abandoned. They hope to identify Ruby’s biological mother with UNIT technology.
Ruby and Rose go to Ruby’s apartment to get the tape. Ruby’s adoptive mother Carla (Michelle Greenidge) returns with them to UNIT HQ, leaving Carla’s aging mother Cherry Sunday (Angela Mynter) with their neighbor, Mrs. Flood (Anna Dobson). After they leave, Mrs. Flood treats Cherry with contempt and watches a coming storm, saying, “He waits no more.” Ruby and Rose return to UNIT HQ and, with the Doctor, use a Time Window to recreate the night Ruby was abandoned, along with UNIT’s Colonel Chidozie (Tachia Newall). A dark hooded figure who may be Ruby’s mother points toward the Doctor and vanishes as a mysterious swirling vortex appears where Chidozie stood. The Doctor, Ruby, and Kate try to rescue him but the window overloads, leaving Chidozie’s withered remains behind.
The Doctor goes with former companion Melanie Bush (Bonnie Langford) to talk to Triad. He does not recognize Triad as his granddaughter and realizes that she has dreams of other existences. UNIT views the vortex on the tape and find that the TARDIS was at the center of the vortex. Something surrounding the TARDIS begins to groan. A member of UNIT named Harriet Arbinger (Genesis Lynea) is identified as an agent of The One Who Waits, who is Sutekh, the God of Death and an old enemy of the Doctor. Triad breaks down over her memories of her dreams and Sutekh possesses her and tries to kill the Doctor.
The episode was directed by Jamie Donoughue and written by Russell T. Davies, who got the idea from a Doctor Who episode 40 or 50 years ago. It ties together all kinds of loose threads and previous stories, particularly 1975’s Pyramids of Mars with Tom Baker as the Doctor. Sutekh is the Egyptian god Set. This is the first part of a two-part story, climaxing with The Empire of Death.
Susan Triad Technology is abbreviated as Sue Tech or Sutekh. Nicholas Briggs is the voice of Vlinx the intelligent robot. Briggs is best known as the voice of the Daleks, the Cybermen, and the Judoon. Sutekh is voiced by 91-year-old Gabriel Woolf, who also voiced Sutekh in The Pyramids of Mars. The episode garnered 93% on Rotten Tomatoes but had the lowest viewing numbers of the series.