Kate Stewart

Kate S. Lethbridge-Stewart, also known as Kate Stewart, was the Chief Scientific Officer of UNIT. She was the daughter of Alistair Gordon Lethbridge-Stewart and his first wife Fiona, and the mother of Gordon Lethbridge-Stewart and another child.

Kate spent her youth not knowing of her father's activities with extra-terrestrial beings, believing whole-heartedly that his life consisted of a boring and simple military job. She and her mother spent much time ironically joking that he was constantly off on amazing adventures when they both knew the "truth." Kate would not begin to scratch the true surface of her father's life until years later when she shared an encounter against the Great Intelligence with him. She would spend some time investigating UNIT and her father's ties to it, at one point encountering ex-UNIT operative Douglas Cavendish to investigate a "haunting," which revealed itself to be a Dæmon. She soon joined the organisation, rising to its top position and changing it to be a more scientific, peaceful group.

As the leader of UNIT, Kate encountered the Doctor many times during encounters between Earth and alien threats, becoming similar to the Doctor as her father had been. She was at the forefront of the peace treaty between humanity and Zygons on Earth.

Childhood
Kate S. Lethbridge-Stewart (PROSE: Christmas on a Rational Planet) was born to Fiona and Alistair Gordon Lethbridge-Stewart, three years into their marriage, which lasted eight years. (HOMEVID: Downtime)

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)

She would sometimes have nightmares about seeing monsters in her room at night. On another occasion she found herself lost in a forest without her father being able to find her. (AUDIO: Narcissus)

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)

At the age of seven, Kate saw the Fourth Doctor and Sarah Jane Smith at the UNIT Research Institute but did not interact with them. She was confused when her father told her the Doctor was both a genius and an idiot. (PROSE: The Day of the Doctor)

John Benton met Kate as a child, and called her "little Katie". (AUDIO: Call to Arms) It may have been around this time that Kate spent some time with her father at Ealsdon House in Scotland. She became friends with Ben Donelly for a while, the two of them would regularly run up and down the long gallery singing a nursery rhyme about a ghost that haunted the place called the Grey Man. (AUDIO: Invocation)

Adult life
Eventually, Kate grew estranged from her father, with her mother blaming her father for their separation. (HOMEVID: Downtime, PROSE: Of the Future) By 1989 she was a student at a college in Reading, having left home to get some independence, and shared a house with her best friend, Cecilia Hunter. She became attracted to her science teacher, Jonathan James, and was surprised when she discovered he shared the attraction. They began dating, despite college rules, and in December of that year she discovered she was pregnant. So as not to ruin Jonathan's career, Kate opted out of college. They paid a visit to Kate's father, to tell her she was pregnant, but after witnessing an attempt on the Brigadier's life, Kate realised she could not bring her son into her father's life. She left without telling him of her pregnancy. (PROSE: Of the Future)

On 25 September 1990, she gave birth to a son, whom they called Gordon James Lethbridge-Stewart. When Jonathan queried the name, she explained the Gordon was after her grandfather, and the James was after Jonathan. (PROSE: Of the Future, HOMEVID: Downtime) 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, which Kate had originally lived on with Jonathan prior to Gordon's birth. (PROSE: Of the Future)

Because the cult based at New World University believed she might be able to lead them to the Brigadier, who 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) Over the years she became close to her nephew, Conall Lethbridge-Stewart, who was also extremely close to Gordon. (PROSE: Acceptance, and then Understanding)

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 October 2003, 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 Dæmons — 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)

By September 2004, Kate and Gordon lived in a house in Streatham, London, although they often still used the old canal boat. After both Gordon and Conall were kidnapped at Gordon's fourteenth birthday party, Kate and Cavendish sought the help of Kate's father. (PROSE: Downtime: Child of the New World)

Kate later married, had a second child, and got divorced. (TV: Death in Heaven) In December 2011, Conall sought her advice in buying Gordon a Christmas present. On Friday 16 December, Kate visited her father with her step-mother, Doris, and her brother, Albert. When they left to get hot drinks, Kate was left alone with her father. He spoke about the Doctor, the laws of time, and about when he or she would come to visit. (PROSE: Lucy Wilson and the Bledoe Cadets) Doris, Albert and Kate were present when he died later that day. (PROSE: Acceptance, and then Understanding)

On Saturday 7 January 2012, Kate attended her father's funeral. She stood next to Lucy Wilson as heartfelt hugs were given. (PROSE: Lucy Wilson and the Bledoe Cadets)

She dropped the name "Lethbridge" when she joined UNIT so as to be judged on her own merits and not be perceived as being the beneficiary of nepotism. (TV: The Power of Three)

Meeting the Doctor
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". 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)

Stopping a Nestene invasion
Kate invited Osgood to Simon Devlin's demonstration of a 3D printer, where she met with Jacqui McGee who knew who she was. She was concerned that the technology could be used for war applications. (AUDIO: Vanguard) She later sent Sam Bishop to the Gobi Desert with Osgood to search for a Swarm Leader. She then met with Devlin to find out more information about him to see if he was connected with the Nestene Consciousness. (AUDIO: Earthfall) Kate asked Osgood to examine the energy unit and the 3D printer, and was later kidnapped by Devlin, who wanted to convert her into an Auton. (AUDIO: Bridgehead) Bishop sent her to Black Archive 5 to find an item the Ninth Doctor used against the Nestene, anti-plastic. She then went to Devlin Futuretech to buy some time for Osgood and to learn more about the Nestene's plan. (AUDIO: Armageddon)

Tengobushi incident
She got angry when she discovered that Lyme Industries had taken some of UNIT's property under Peter Latcham's orders. She tried to get it back in a covert mission but she discovered that Lyme Industries had taken it all to their headquarters. (AUDIO: Power Cell)

She went to Geneva to get head office to authorise an investigation into the leak in the UK Government and the Tengobushi attack. She got annoyed when Grant Avary called the UK Government to inform them of Kate's actions. After an attack happened on a French mountain near Geneva she helped Avary to investigate. Discovering that it was similar to the attack in London she managed to persuade Avary that she was right. When Avary was captured by the Tengobushi she devised a way for her and Osgood to get inside the ship to aid his escape. She then went back to London to stop Dokan getting into the Tower of London to get the Kamishi energy cell. (AUDIO: Death in Geneva)

She and Osgood had to fly the plane they were on after the Tengobushi killed their pilots. She asked Josh to kidnap Lyme in order to get information on the artefact the company had. She met with Dokan to find out why he wanted the energy cell. She tricked Dokan into meeting her in the Tower and then let a bomb off to destroy the Kamishi energy barrier. (AUDIO: The Battle of the Tower)

She was placed under arrest by Latcham, but was later freed by Osgood and Carter. With the experimental aircraft at the base she went to rendezvous with Bishop in South America, and then travelled to Antarctica to uncover Lyme's generator there. She confronted Lyme and told her the consequences of using alien technology. When the Kamishi arrived to take their technology back, she managed to persuade them not to kill everyone who had knowledge of their technology but use their mind wipe chemicals instead. Back in London she took delight in personally removing Latcham's memory. (AUDIO: Ice Station Alpha)

Investigating the Silence
She decided to up her training of shooting and asked Carter to help her. She put Shindi on undercover observations at Helena Faversham's place to uncover the strange energy readings Osgood was detecting. She was concerned about the conspiracy theorist. She posed as part of the charity commission to talk to Faversham. She tried to negotiate with the Silents but they wouldn't do it. (AUDIO: House of Silents)

She forgot the whole incident with the Silents, though could remember going to Faversham's house. Jacqui got her to remember the investigation and with Osgood and Bishop's help they found the evidence. She found out that the Silents were influencing the UK population to trust Kenneth LeBlanc and that Carter had been brainwashed too. (AUDIO: Square One)

She found it disconcerting about Carter's involvement in the resignation of the PM and that she had to remind her troops about the Silents. When Bishop showed her the moon landing footage with the Silents in them, she realised that it must have been the Doctor who put it there. Kate became suspicious when the Silents got Carter to order a high amount of explosives. She thought that they were planning to assassinate both LeBlanc and the outgoing Prime Minister, as she thought that this was the best way to get media attention and overrule the Doctor's message to kill them all. (AUDIO: Silent Majority)

She was concerned after they lost contact with Osgood and Bishop on the UNIT satellite. She was trying to investigate the cause of the loss of communications. She discovered that the Silents were manipulating the powers of the world to the brink of starting a war with each other. After she realised that the Silence were also provoking the Telokni to fire on the UNIT space station, she used the footage of the destruction cut with the Silents saying they were leaving the Earth, using McGee's editing skills to do it. (AUDIO: In Memory Alone)

The Silurian invasion
Kate and Osgood investigated a Silurian nest at Scafell when they started to attack. She and Osgood escaped and made their way to John Benton's pub. Whilst there she was aided by Benton and Mike Yates, to help defend herself against the Silurians. She couldn't leave Benton behind when he became injured and stayed when Osgood and Yates left in Bessie. After the base was destroyed she asked them to come to London for a debrief. (AUDIO: Call to Arms)

Kate later went to find Jo Jones for a mission, and discovered her chained to a factory protesting the pharmaceutical industry. After 'Project Charybdis' went off course she immediately went to help them. She almost destroyed the Sea Devil base, but Osgood stopped her. (AUDIO: Tidal Wave)

Osgood and Kate made their way to a Silurian nest in Greece to find a control device for the hybrids that Anthony Burmaster had released. She made her way through the base but was attacked by Tryska and poisoned. Fortunately she was rescued by Bishop and given a broad spectrum anti-venom. Whilst in the base's computer room she managed to find information on the variation of the Silurian and Sea Devil species and where she could find some anti-venom. (AUDIO: Retrieval)

She was still recovering from the poison by the time she managed to get back to the UK. Kate passed local control of UNIT in the UK to Mike, Benton and Jo due to their experience with Silurians and Sea Devils, whilst she couldn't get back to base. Kate sent Sam to a weather station to brew up a storm off the coast of the UK. This caused the Silurians to slow down and neutralised their forces. She tried to negotiate their surrender by allowing them to go back into hibernation. She later put Jastrok and Kalana into hibernation under the Black Archive so that their people could punish them. (AUDIO: United)

Brief Encounters
Kate and her team flew to South America on intelligence that a local resistance force had obtained alien technology. There they met resistance leader Captain Maria Gonsalves and discovered she had a captured Dalek in her secure bunker. Kate was able to purchase the main body of the Dalek, but not the armaments which she originally believed was part of the deal. When the Dalek revealed that there were others of its kind in the surrounding jungle, Kate and Shindi took the Dalek creature to find the other Daleks, but the creature escaped. Returning empty-handed, Kate was taken prisoner and together with Osgood, discovered that Gonsalves was part of a worldwide auction house of alien technology and weapons. Having re-entered its casing, the Dalek killed Gonsalves and self-destructed, destroying the bunker. Having escaped the explosion, Kate and her team were then rescued by the American arm of UNIT. (AUDIO: The Dalek Transaction)

Noticing an irregularity in UNIT’s paperwork, Kate headed to Ealdon House in Scotland, a research facility set up in her father’s time but abandoned soon after. There she met Ben Donelly, the caretaker, and his mother Alice. Kate’s memories of visiting the house soon returned to her as well as the unsettling nature of the long gallery. Entering there again she had another encounter with the supposed Grey Man and was nearly frightened out of her wits. After recovering, Kate was joined by Osgood and Josh and discovered Alice had discovered a particular resonance in the house that induced fear in the humans. She had wanted to harness this resonance as a weapon before Kate’s father stopped her. With an unknown alien presence drawing near, responding to a message Alice left years ago and hearing of mass outbreaks of terror in the capital, Kate and Osgood deciphered and completed the message, averting the crisis. (AUDIO: Invocation)

Kate observed Shindi's arrival in the Ardennes, via the hologram projector, and his discovery of a Sontaran capsule. Suddenly, they were ambushed by a squad of Sontarans and Kate lost contact with Shindi. Later when he and the Sontarans returned to England, Kate and some UNIT troops met up with them outside the Torrence Research Foundation, having tracked them using the hologram projector. Allying themselves with the Sontarans, UNIT stormed the building and found Osgood held captive. They also uncovered a group of Sontarans cloned by Professor John Torrence, who hoped to sell them off as warriors for hire in the worldwide auction. While shutting the operation down, Kate learned from Christine Colley about the mysterious head of the auction, the Overseer. (AUDIO: The Sontaran Project)

Kate was worried when an experimental travel capsule, obtained from the auctioneers, suddenly vanished from Osgood’s lab taking her and Josh with it. On their return Kate was bemused by how familiar Josh and Osgood had become with each other. She soon realised this Osgood was in fact from a sideways dimension where UNIT was run by a fascist state. With the other Osgood on the run, while armed and dangerous, and the real Osgood returned, Kate was the only one to realise this, preventing Shindi from taking the real Osgood prisoner. Soon the other Osgood returned and attempted to escape again in the capsule. Kate and her team were saved when the capsule managed to disappear just before the dimensional gateway imploded. Kate then informed her team that Sam had more information on the auctioneers and they were to report to her office. (AUDIO: False Negative)

The Auctioneers and the Cyber Invasion
She went with Osgood to find and rescue Bishop from the Auctioneers. At the Auctioneers' facility they were contacted by the Overseer. They then received information that led them to Bristol. She became worried when one of the puzzles involved Heathrow Airport. The Overseer was punishing her for what UNIT had done to their organisation. Kate was warned to keep away from the Auctioneers. (AUDIO: Game Theory)

Kate wanted to get the Auctioneers app pulled from the app stores and deleted from everyone's devices but there was resistance. She monitored Osgood, Shindi and Carter when they went into the virtual world. She was shocked when trying to disconnect the VR equipment from her colleagues. She then went to get more equipment in case she needed to try again. She tried to shoot the Cyberman. (AUDIO: Telepresence)

Kate declared a Code Silver. She then placed Fortress Island under lock-down. Kate knew of the reasons why the Cybermen were created in the first place and it worried her. She initiated a communications blackout to stop the Cybermen. She went to the armoury to get anti-Cybermen weapons that UNIT had developed. She dissected a Cyberman and she thought that the Cyberman's head handles were used to conduct energy. After the Auctioneers app was placed on everyone's phone, she decided to activate the nuclear weapon under the base. (AUDIO: Code Silver)

arrived and disarmed the weapon, requiring some components from the UNIT archives to repair his TARDIS. When the Cybermen took the Master's TARDIS, Kate accepted his "offer" to help defeat the Cybermen. She went with him and Carter back to the UNIT base but her helicopter was hijacked by the Auctioneers. After the Master killed the Auctioneers, she used the weapons held there to destroy the Cybermen that came after her. She watched over the Master whilst her plans were being undertaken, and conversed about her father. She realised that if her plan to destroy the Cyberman failed she would have to kill Osgood. She was slightly worried when the Master became partially Cyber-converted but was glad when he wasn't and wiped the Cybermen out. She pleaded with the Master to stop millions dying, and allowed him to escape once he undid his back-up plan. (AUDIO: Master of Worlds)

A Wirrn incursion and encounters from UNIT's past
She was concerned when the Master left them a parting gift. She later welcomed Shana Siddiqui to UNIT. After the Wirrn escaped she went to Geneva to warn her superiors. She tried to communicate with the Wirrn after they infected Marcus. When the Wirrn eggs hatched she didn't want to blow up the base. She was too late to detonate the base as the Wirrn had disabled the function. The Wirrn wanted to negotiate with her. She asked Shana to discover what had killed the Wirrn in the past. (AUDIO: Hosts of the Wirrn)

She went on a date with Richard which was interrupted by a skyfall incident. She was intrigued at their communication strategy. She wasn't sure that Vara was telling the truth but wanted her to fire a warning shot. She then wanted to listen to the apparent invaders. She was angry that Vara was threatening the lives of the planet. She decided to hand Vara back to her people, though she wasn't sure of this decision. She tried to convince Jarrak not to kill Vara. She rescinded her agreement but Jarrak went on a war footing. (AUDIO: Breach of Trust)

The Ministry of Defence told UNIT that they should use the Pandora Institute as part of their training to make better soldiers. Kate was sceptical of this and went there with Osgood and Carter to investigate. On the island she told Osgood part of this was because of the spate of deaths of people who had visited the institute. She overheard a conversation by its founder Chin Lee and went to find this container one. When she met with Chin Lee, she was told that she wanted to go under treatment but she couldn't remember it. Her biggest fear was to lose her team. She confront Lee about the deaths. She wanted to know what she was doing back in the country. Once the creature was defeated she thought that UNIT should have done more to help Chin Lee after the Master's influence was taken away from her. (AUDIO: Open the Box)

Alien Incursions
She took Osgood and Josh to Abbey Marston in order to resurrect Warren Calder and find out where he hid the Silurian plague that he claimed to have stolen shortly before ending his own life. This was revealed to be a ruse by Calder who wanted Kate to resurrect him in Abbey Marston so that he could use the stone circle to steal a new body and cheat a terminal illness that he had been diagnosed with. However, in doing this he released the static, who planned on stealing bodies of their own so that they could exist on Earth. They were defeated by Kate, Osgood, Josh and Calder when they destroyed the stone circle. (AUDIO: This Sleep of Death)

Kate oversaw Osgood and Sam Bishop's investigation of the unusual weather conditions revealed to have been caused by the Animoi. (AUDIO: Tempest)

Temporal anomalies
While investigating temporal anomalies along the Dorset coast, Kate discovered records of a similar incident in 1972, which stated that Jo Grant would give her life to save the world, prompting her to request Jo's assistance. During the investigation, Jo and Kate were pulled through one of the rifts and sent back to 1972, where they met the Third Doctor as he investigated the original anomaly. In an attempt to preserve the timeline, Kate just introduced herself as the head of UNIT in the future, and she and Jo assisted the Doctor in setting up the equipment to shut down the anomalies. While the Doctor and Jo went off to have a meal, Kate was tricked into reprogramming the Doctor's equipment by a voice posing as Osgood from the future. As the Doctor devised a new solution, Kate was convinced to explain the situation to her father over the radio, as the Doctor had worked out her true identity. Although she never revealed her true name, Kate told her father that it was an honour to work with him, and briefly broke down sobbing when her father ended the call by telling her that the future of UNIT was clearly in good hands. After the anomalies were stopped when Jo apparently sacrificed herself, Kate returned to the future, where she and Osgood received a letter from the Doctor which gave them the necessary equations to retrieve Jo from the Time Vortex. (AUDIO: The Sacrifice of Jo Grant)

She investigated her own murder when her body was discovered within a power station. She was suspicious of the director, known as River Song. However the director was in fact a Wampeerix Battle Queen masquerading as River Song, intent on feeding off the energy of the Earth. The real River Song aided Kate and Osgood in defeating the Wampeerix. (AUDIO: The Power of River Song)

Trouble at the National Gallery
UNIT had in its possession a picture of Kate with River Song whilst the latter was wearing her Demons Run garb, as well as a photo of Kate with Clara from her "previous visit". (TV: The Day of the Doctor)

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 a time 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 doppelgangers in the Black Archive. Kate ordered the countdown to detonate the Archive with a nuclear warhead which would not only prevent 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 War, Tenth and Eleventh Doctors triggered the Black Archive's 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)

Actions with the Twelfth Doctor
In 2013, UNIT lost one of their lead scientists, John Foster, who died in a car accident. Kate and the team spent the next year trying to reactivate the projects (based off of the technology left by the Cybermen in 2007), but found various codes that blocked access. She visited the home of Foster's family, who were having trouble coping with the accident. It was then that another John Foster broke through into their dimension to meet with his daughter, unbeknownst to them. When London was attacked by a species originating from the void known as the Fractures hunting Foster, Kate aided the Twelfth Doctor and Clara Oswald in pushing back against the aliens. (COMIC: The Fractures)

When the Cybermen emerged from St Paul's Cathedral in the 21st century, Kate arrived with Osgood and UNIT and took and the Twelfth Doctor into custody. She told the Doctor that he was President of Earth and worked with him to battle the Cybermen. When the Cybermen attacked the plane Boat One under Missy's command, part of the fuselage blew off and Kate fell out. She was saved by her father, who had been converted into a Cyberman, and returned safely to the ground. (TV: Death in Heaven)

After the Hyperions had conquered Earth, Kate led the population of London underground until the Doctor arrived and managed to defeat the invaders. (COMIC: The Hyperion Empire)

When Missy returned and froze all the planes on Earth, Clara came to UNIT and Kate helped her contact Missy. (TV: The Magician's Apprentice)

Kate and UNIT went to investigate a Zygon invasion that broke out after a splinter group decided a peace treaty with humans was unacceptable. She was determined to bomb the rebel Zygon settlement, but the Doctor convinced her that this would only make the situation worse – threatening to radicalise every peaceful Zygon on the planet.

Kate followed a lead to Truth or Consequences in New Mexico to try and find the root of the uprising. Here she encountered the one remaining inhabitant of the town, police sheriff C. Norlander, who explained how the trouble started – the accidental revelation of a young Zygon in true form who "hadn't learnt to preserve his body print" had caused panic, distrust and violence within the human population. As the truth of what had really occurred began to dawn on Kate, she realised that Norlander was, in fact, a Zygon rebel agent. (TV: The Zygon Invasion)

She was then attacked but managed to kill the Zygon, before taking its place to fool the High Command. Kate was present in the Black Archive when the Twelfth Doctor forced her to become an ambassador for the human race in an attempt to negotiate a new peace treaty alongside the Zygon High Command leader Bonnie in which a standoff occurred involving the Osgood Box. However, her memories of the Box were soon erased. (TV: The Zygon Inversion)

Along with the Osgoods, Kate watched Daniel Claremont's speech at Ravenscaur School where the Prime Minister was revealed to be a Sea Devil who launched war on the world from Scotland. Though Kate quickly ordered a UNIT fleet against the Sea Devil warships, the Doctor ordered her to pull the ships back, knowing them to be no match for the Sea Devils. (COMIC: Clara Oswald and the School of Death)

After Jenny's bowship had crashed into the Terrance Dicks Library at St Luke's University, Kate issued a D-notice as UNIT began cleaning up the wreckage. The craft was saturated in Void energy however and all of UNIT wound up possessed by the will of a maddened Type 1 TARDIS, being driven to attack the Doctor before the threat was handled. As the Doctor led Bill and Nardole away, he left Kate to resume clean up operations. (COMIC: The Lost Dimension)

UNIT shutdown
In 2018 UNIT was dealing with budget issues brought on by Brexit. Kate should have been leading the operation to deal with a change in time in the year 1896, but her team were busy elsewhere, meaning that Anne Travers and Bill Bishop were taken out of retirement to deal with it. (PROSE: An Ordinary Man)

By New Year's Day 2019, UNIT operations were still suspended due to financial disputes, and the Thirteenth Doctor was unable to contact Kate about an ongoing Dalek threat. (TV: Resolution)

Kate still didn't work for UNIT in 2020. (PROSE: The Invasion of London, WC: 14684 UNIT Field Log)

Kate attended Sarah Jane Smith's memorial on a "bright, cold Spring day", where she discussed Sarah Jane with other guests, giving Sarah Jane's son Luke "the biggest hug", and helped fight the Jackals of the Backwards Clock to foil the Trickster's revenge plot. (WC: Farewell, Sarah Jane)

The remains of UNIT began to deal with the Time Fracture at a former Black Site. On 8 August, 2020, after receiving a list of names who could help with the operation from the Doctor, Kate sent out a message to one of the individuals, breaking security protocols, as she was no longer head of UNIT. (WC: 14684 UNIT Field Log)

Personality
Kate disliked the use of weapons, refusing to take a gun from Sarah Jane Smith when offered. (HOMEVID: Downtime) When she took over UNIT, she enacted great changes to favour scientific approaches over military means. (TV: The Power of Three)

Kate believed that "Science leads", (TV: The Power of Three) though "science needs to remember to carry a gun sometimes." (AUDIO: House of Silents)

She believed herself and Osgood to be UNIT's greatest scientific minds. (AUDIO: Retrieval) She usually let Osgood use the call sign Greyhound Two. (AUDIO: Call to Arms)

She refused to treat her people as pawns, but when dealing with the Master, recognised that it was more important to define deaths based on the loss of practical resources and potential allies as appealing to the Master on moral grounds would be pointless. (AUDIO: Master of Worlds)

Kate disliked Elizabeth II's name being used as a nickname for the Wirrn Queen. (AUDIO: Hosts of the Wirrn)

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 Doctor Who television 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 debut of Prof Arthur Candy who originated in the spin-off short story, Continuity Errors.
 * Jemma Redgrave, who is naturally a brunette, plays the role of Kate with blonde hair matching Beverley Cressman's portrayal of the character.
 * The in-universe article A Brief History of the Lethbridge-Stewarts, available as a download from the Lethbridge-Stewart website, says Kate joined UNIT in 2004, following Daemos Rising, at the behest of her father. Because it is non-narrative, it is not a valid source on this wiki.