Constance Clarke was a leading WREN of the Women's Royal Naval Service during World War II, working at Bletchley Park in 1944, who travelled with the Doctor in his sixth incarnation. She preferred to be addressed as "Mrs Clarke".
She had a great-uncle named Jasper, who lived alone in an expansive manor house and spent his time talking to his dog and taking potshots at rabbits. The Doctor reminded Constance of him. (AUDIO: Shield of the Jötunn)
She returned to the United Kingdom after her father died of tuberculosis prior to 1940. Constance attended Somerville College at the University of Oxford, where she received a first in modern languages. At a young age she married sub lieutenant Henry Clarke of the Naval Intelligence Division, who was posted to special duties in November 1943. They were unable to have children. (AUDIO: Criss-Cross, Quicksilver)
Solo travels with the Sixth Doctor
In 1944, she met the Sixth Doctor when she chastised him for overworking Sylvia Wimpole. When Major Harris came to investigate information on the Doctor, she asked him about her husband and if he was still alive. She accompanied the Doctor to Cambridge and asked Robbie Flint about her husband as well. She forced the Doctor to take her with him on his travels, wanting to be taken back to her duties once she decided to finish travelling. (AUDIO: Criss-Cross)
Constance went through the Doctor's email in-box and found several emails for the Rani's parole hearing. She visited Teccaurora Penitentiary when the Rani kidnapped her. Raj Kahnu asked her why she travelled with the Doctor and then tried to have her placed in one of his suits of armour. (AUDIO: Planet of the Rani)
On one travel with the Doctor, she visited the Parallel Sect where she rescued Tim Hope from being run over by a train. She suggested that they should get back to the train station when she saw the remnants of the driver's cabin. The Doctor left her in the train when he went with Keith Potter to look after the passengers. After Alice LLoyd started acting strangely, Constance left with Tim to find the Doctor. Arriving at the station, she informed the Doctor that the passengers were killing each other like it was an epidemic. The Master threatened her with his Tissue Compression Eliminator. She was delighted when the Doctor defeated the Master's plans. She had Tim's coat on which contained a Relative Dimensional Stabiliser. (AUDIO: The End of the Line)
Travelling with the Sixth Doctor and Flip
Given that she was married, when the Doctor introduced her to others as "Constance," she was quick to correct the Doctor to a more formal "Mrs Clarke." (AUDIO: The End of the Line) However, she allowed Lyam Yce, Florrie Solomon and Ammar Elkady to address her by her first name. (AUDIO: Absolute Power) She initially disliked it when Flip Jackson called her "Connie" but she eventually came to tolerate it. (AUDIO: Quicksilver)
Behind the scenes
Constance first appeared in The End of the Line as an existing companion of the Sixth Doctor. Due to the release date of The Sixth Doctor: The Last Adventure being changed from September 2015 to August 2015, The End of the Line was released before the character's introductory story.