The Doctor

At UNIT’s London Headquarters the TARDIS arrives and on exiting The Doctor and his travelling companion Ruby Sunday are met by UNIT’s leader Kate Lethbridge-Stewart and several other members of UNIT including Colonel Ibrahim, the Vlinx, Rose Noble, Harriet Arbinger and new scientific adviser Morris Gibbons. With introductions complete The Doctor asks Kate to help him to try and identify the mysterious woman who has appeared numerous times in his recent adventures. UNIT however, already know who this woman is. She is called Susan Triad, the head of S Triad Technology and UNIT have been monitoring her for some time. They are also aware that she is currently preparing for a world-wide announcement to unveil new technology that she intends to give away. UNIT believe that S Triad to be an anagram of TARDIS, and so believe it to be a trap. The Doctor though additionally believes that Susan Triad may be his granddaughter, Susan. Kate also reveals that when Susan Traid changed her company's name, to S Triad Technology two months ago, Kate assigned Melanie Bush to monitor her as an undercover agent on the press team, but she has not found anything extra-terrestrial about Susan Traid.

The Doctor then reveals another mystery that he would like to resolve - this being the unknown identity of Ruby's birth mother with the only point in time he encountered her was Christmas Eve in 2004 when saving Ruby from the Goblin King (see "The Church on Ruby Road"). When it is suggested that The Doctor just go back in time, he explains that because he travelled there in the TARDIS once before, he has time locked himself from the event and so they need a different method because he is not able to cross his own timeline again. Harriet Arbinger suggests they use CCTV footage that was captured at that time. Ruby reveals she has one of the original VHS tapes but along with her adoptive mother, Carla Sunday, they have been unable to work out her mother's face. Morris Gibbons reveals that they can use UNIT's technology to enhance the video and so identify her. Excited, Ruby heads with Rose Noble to Carla's flat to collect the VHS tape.

While Ruby is away The Doctor is reading through information about Susan Triad when Kate begins talking about her father, Brigadier Alistair Gordon Lethbridge-Stewart, and how The Brigadier and The Doctor used to have so many adventures together. Melanie then arrives and The Doctor enthusiastically hugs her. Melanie has managed to obtain a sample of Susan Triad’s DNA but when this is analysed Susan Triad still comes up as being human. Ruby and Rose, along with Carla, then return with the VHS tape. The Doctor asks Kate to use UNIT's Time Window so that they can project the tape's memory of the past as this will enable them to see the image of that night as if they are actually there. Kate tries to claim that they do not have one as per the Third Doctor's warnings that they never tamper with time travel technology. But The Doctor's insistence forces her to reveal they do actually have a Time Window.

Kate Lethbridge-Stewart

They arrive in the Time Window, a large open space separated by glass from high-tech desks. The Doctor is initially amused at the primitiveness of UNIT’s time travel efforts compared to his own. He soon though takes command, leading Ruby into the middle of the open space along with the head of security for the Time Window, Colonel Winston Chidozie. Morris Gibbons setups up the VHS tape while The Doctor asks Ruby to tell him again about the story of her abandonment. As Ruby tells him, snow starts to fall within the room. Kate and Morris are astounded because they have not activated the Time Window yet. Eventually, The Doctor permits them to do so and the machine blazes into action.

As the VHS tape plays a lifelike projection of Christmas Eve in 2004 appears with Ruby and The Doctor in the middle of it. The projection even produces the sound of the Carol of the Bells coming from the church. Then they spot the hooded figure, that is believed to be Ruby's mother, but they are unable to see her face. As she approaches Ruby tries to touch her, but The Doctor holds her back as they can't risk changing the timeline. The woman then stops and suddenly, the TARDIS' hum springs to life. The Doctor from the past has arrived and proceeds towards the church to defeat the Goblins. The Doctor then turns back to the hooded woman, but feels his memory of the event changing. The hooded woman then points at The Doctor. Confused by this The Doctor asks Colonel Chidozie to see if there was anything else the figure could be pointing at. But Colonel Chidozie sees nothing as he walks out of sight behind the image of the TARDIS. The hooded woman then turns away and vanishes, devastating Ruby as they still do not know her identity. Then on schedule, the past Doctor returns. He enters the TARDIS which then dematerialises. However, to everyone surprise Colonel Chidozie is not behind where the TARDIS once stood. Instead, a mysterious swirling vortex of black sand and orange particles appear where the TARDIS once stood. The Time Window then overloads, leaving behind Colonel Chidozie's aged and dead body, covered in sand. While an angry Kate deals with the dead body, The Doctor turns to Melanie and orders her to take him to see Susan Triad.

Melanie Bush

The Doctor and Melanie arrive at Triad Technology as Susan Triad is about to start her international technology launch broadcast. The Doctor soon realises that Susan Triad is not his granddaughter as he does not feel any Time Lord essence from her. On questioning Susan Triad, she remarks that she is so busy and struggles to sleep. The Doctor asks her about the people she dreams about, his suggestions of Lindy Pepper-Bean and the Villengard ambulances appearing to awaken memories within her. Susan Triad then leaves to carry out her broadcast but The Doctor decides to stay so that he can monitor her. Meanwhile UNIT view the vortex on the VHS tape and, using image enhancing technology, are able to determine that another TARDIS was at the location of the church and it was at the centre of the vortex. They then identify a large invisible being surrounding the TARDIS in the command room. Kate contacts The Doctor, informing him about the entity potentially controlling the TARDIS - as a groan emits from The Doctor’s time machine. After scanning the TARDIS a large beast begins to manifest in the command room. The Doctor orders Kate to send Ruby back to the Time Window, while Kate and the others confront the entity that is now towering over the TARDIS. Back in the Time Window, Ruby is sent back to Christmas Eve in 2004 and once again she witnesses the hooded woman walking towards her.

Back in UNIT’s command room Harriet Arbinger is revealed to be a harbinger of The One Who Waits who is revealed to be Sutekh, The God of Death. On hearing this The Doctor realises that they were looking at the wrong anagram, as when the anagram of Susan Triad Technology is rearranged to form Sutekh's name (Sue-tech). Meanwhile during her broadcast Susan Triad breaks down over the memories of her dreams. She then transforms into a terrifying undead-like monster that brings ‘the gift of death’. In shock, The Doctor can only stand, rooted to the spot, as Sutekh announces that now he is free he intends to bring death to The Doctor and all life in the universe.

Melanie helps The Doctor flee from Susan Triad as she and Harriet Arbinger start to kill everyone by releasing dust clouds of sand. As the clouds spread, all those in London, then the whole of the UK, soon followed by the whole of planet Earth, succumb to Sutekh's dust of death. This includes Kate, Rose Noble, Morris Gibbons as well as Carla and Chery Sunday and Mrs Flood. The Doctor and Melanie though manage to escape and are reunited with Ruby in the Time Window as Sutekh arrives on top of The Doctor's TARDIS. Sutekh reveals that when The Doctor defeated him when they last met (in the 1975 Fourth Doctor story "Pyramids of Mars"), instead of being defeated Sutekh latched himself onto the TARDIS and has travelled to every planet that The Doctor has visited - growing more powerful with every journey. Sutekh explains that the dust is spreading through every place the TARDIS has ever landed through copies of Susan Triad.

Ruby Sunday

The Doctor realises he can use the TARDIS, in the Time Window, to create a Remembered TARDIS featuring objects from across The Doctor's history which, along with Ruby and Melanie, he can use to flee from Sutekh. The Doctor uses special ‘intelligent rope’ to stabilise the Remembered TARDIS. He also deduces that Sutekh is only keeping them alive because he is also interested in the identity of Ruby's mother. He visits a woman who gifts him a spoon which he uses to repair a monitor from the Time Window. The monitor responds to Ruby's memories and it shows her a 2046 interview with Roger ap Gwilliam (a person that The Doctor once said, in "73 Yards", was the ‘most dangerous Prime Minister in history’). The Doctor realises that while Prime Minister, Roger ap Gwilliam made DNA tests compulsory and so this will enable them to find Ruby's birth mother.

The Doctor uses the Remembered TARDIS to visit, along with Ruby and Melanie, 2046. However, while The Doctor and Ruby search the DNA records for Ruby's mother, Melanie is turned into a servant of Sutekh and they are all transported back to UNIT’s London Headquarters. On arrival Sutekh attacks The Doctor and to make him stop Ruby confronts Sutekh saying that she will show Sutekh the name of her mother. Ruby though, on approaching Sutekh, instead destroys the monitor containing her mother’s identity and attaches the intelligent rope to his collar. The Doctor uses a whistle to activate a rocket booster in the TARDIS console, bringing it towards him and vaporising Harriet Arbinger in the process. He attaches the other end of the rope to the TARDIS console, dragging Sutekh through the time vortex, forcing him to undo all the deaths he has caused, including Kate, Rose Noble, Susan Triad, Mrs Flood and Ruby's mother and grandmother. The Doctor then kills Sutekh by releasing him into the time vortex, where he is disintegrated.

In the aftermath, UNIT is able to identify Ruby's birth mother, who is revealed to have been a then-15-year-old girl who left Ruby because of her extreme youth and family circumstances. The Doctor explains Ruby's birth mother was a normal woman and that she was only assumed to be important because they believed her to be. The mysterious happenings around Ruby appear to have been the result of Sutekh assuming Ruby's mother held the key to defeating him, unwittingly willing Ruby to be more powerful than she really was.

The Doctor takes Ruby to see her mother and they are reunited. Ruby decides to visit her birth father, and so decides to leave the TARDIS leaving The Doctor to once again travel by himself. As the TARDIS departs, on a roof top, Mrs Flood, dressed in white and with an umbrella, explains to the audience that, while Ruby got her happy ending, The Doctor’s story will end in ‘absolute terror’...