|Job:||Head of Scientific Research|
|Place of origin:||Great Britain|
|Father:||Alistair Gordon Lethbridge-Stewart|
|First seen in:||Downtime|
|Main actor:||Jemma Redgrave|
|Other TV actors:||Beverley Cressman|
Fiona and Alistair had Kate three years into their marriage, which lasted eight years. As a child, Kate was never told of her father's work at UNIT with aliens and was only aware that he was a military man. She would often pretend that he was off to have an amazing adventure when she really "knew" he was off to do boring military operations. (HOMEVID: Downtime)
At the time of the Wenley Moor Silurian incident, Kate was five. It was during this mission that Alistair realised that he was an inadequate father for her. The secretive nature of his work with UNIT prevented him from being consistently present in her life. His long absences from home caused Fiona to leave him. Alistair guessed that she and Kate went off to at least initially live somewhere close to Chichester, the home of Kate's maternal grandparents. (PROSE: The Scales of Injustice)
In her teens, Kate had a son whom she named Gordon Lethbridge-Stewart, thereby demonstrating a continued love of her father, despite her outward ambivalence and her decision not to reveal her pregnancy or Gordon's existence to him. Gordon's father, Jonathan, wanted to marry her, but she wanted to remain single. Jonathan and Kate split up when Gordon was two, leaving Kate to raise Gordon as a single parent. (PROSE: Downtime) Kate and her son made their home aboard a houseboat moored on an English canal.
Because the cult based at New World University believed she might be able to lead them to the Brigadier, whom they thought possessed a locus vital to the Great Intelligence, she and Gordon were harassed by students who staked out her houseboat. Frightened, she reconnected with her father and briefly fought alongside him and Sarah Jane Smith against the New World group. After the Great Intelligence was again defeated, she entered into a friendlier relationship with her dad, and ensured that Alistair could have a relationship with the grandson whom he had not previously known existed. (HOMEVID: Downtime)
In 1997, Alexander Christian used Kate to get in touch with her father. He wasn't allowed to know the Brigadier's number for reasons of security, but he was readily told Kate's (it was 0122 69046). (PROSE: The Dying Days)
In 2004, Kate responded to a message from ex-UNIT operative Douglas Cavendish to investigate a haunting. Arriving at Cavendish's isolated cottage, she faced Mastho, one of the last Daemons — a demonic alien race which her father had previously battled more than thirty years before. They discovered that a future cult called the Sodality had revived, and transported Mastho through time for their purposes. This meant that the threat to the present was neutralised. (HOMEVID: Dæmos Rising)
Her father nevertheless quietly mentored her until his death. He instilled in her the position that "science leads", something he learned from "an old friend" (i.e., the Doctor). Kate eventually rose to the post of Head of Scientific Research, and established UNIT as a military organisation led by its scientists. In this capacity, she summoned the Eleventh Doctor and Amy Pond via his psychic paper to the Tower of London to investigate the mystery of the Shakri cubes. Kate attempted to warn the governments of the world of the cubes when they started their countdown. (TV: The Power of Three)
She ordered the airlifting of the TARDIS to London, to the agitation of the Eleventh Doctor. Kate summoned him there under the royal orders of Elizabeth I, giving him a sealed letter from the Queen and proving her credentials by showing him the impossible painting Gallifrey Falls No More within the National Gallery.
The letter decreed that the Doctor be made curator of the Under-Gallery, and that he be summoned should there be any disturbance there. Kate led the Doctor and Clara Oswald to the scene of the disturbance. There, she showed them more paintings, all landscapes with glass on the floor next to them. When the Doctor jumped through the fissure and met the Tenth Doctor and the War Doctor. Clara attempted to follow him before Kate restrained her.
As she left the room to request important UNIT files, Kate was accosted by a Zygon who had escaped through one of the paintings and then took her image and pretended to be the real Kate to Clara Oswald. Osgood saved her from the Zygon nest. Kate, along with McGillop and Osgood, confronted their Zygon doppelgängers in the Black Archive. Kate ordered the countdown to detonate the Archive which would not only have prevented the Zygons from having control of the many weapons stored there, but would also destroy London in the process. The Zygon used Kate's voice to stop the detonation, but Kate countermanded the order.
Kate and her Zygon counterpart bickered over the detonation, before the Eleventh and Tenth Doctors triggered the memory modifiers to confuse everybody in the room as to whether they were a Zygon or a human. The two Kates stopped the countdown, and negotiated a peace treaty. (TV: The Day of the Doctor)
Behind the scenes
- The character of Kate Stewart was created by Marc Platt for the 1995 direct-to-video story, Downtime. Beverley Cressman portrayed the character. A younger version of Kate appeared in the 1996 Virgin Missing Adventures novel The Scales of Injustice by Gary Russell. She would reappear, again played by Cressman in Dæmos Rising. In 2012 she appeared in the television Doctor Who story The Power of Three, almost twenty years after the character was created. Kate's appearance in The Power of Three marked the first time that a character created for an independent spin-off production appeared in the main series, and followed the on-screen début of Prof Arthur Candy who originated in the spin-off short story, Continuity Errors.
- In The Power of Three, actress Jemma Redgrave, who has naturally brunette hair, appears as a blonde, which matches Beverley Cressman's hair colour in the home videos.