Cate Archer is an agent with Unity.
In the mid-60s when these adventures take place, Unity is an international intelligence organization, the goal of which is to "protect humanity from groups or persons who want to take over the world". It has its headquarters somewhere in England though the exact location is a very closely guarded secret. It performs most of its desired functions through operatives like Archer, as well as the support staff back at HQ, but it does have a paramilitary section that can be called in when major force is needed. While Unity does not answer to any one government, it tends to support the Western powers more. Unity is run by a man known only as Mr. Jones with a Mr. Smith as his right-hand man.
Archer is Scottish citizen, born into nobility as the only child of Lord William Archer and Catherine MacDougal, though the family was actually struggling for money. MacDougal had a horrible birthing experience and died only weeks later. Lord William raised the girl as best he could but suffered from depression and took his own life when she was 14. Still a minor, she was placed into an orphanage but she snuck out one night and never looked back.
To pay her way she learned quickly how to be a pickpocket and a cat burglar, going under the nickname of 'The Fox'. At first she played it low key and just targeted tourists and people foolish enough to be noted as easy pickings. When she neared adulthood, she started working on an as-needed basis with gangs and syndicates, becoming a rather well known - as the Fox - member of the underworld.
Her transition to the spy game came when she stole the watch of an experienced Unity operative name Bruno Lawrie. She did not know that the timepiece was loaded with amenties including a tracker. Lawrie was easily able to locate her and reclaim his property; he also took the opportunity to recruit her. She was intrigued.
Archer's first few missions were all very simple and frankly quite boring, she being the only female in the field and suffering badly from sexism (this is the 60s). It was likely to have remained that way had it not been for a horrible attack by a Unity enemy which resulted in four top agents being killed and Archer given the chance to assist in bringing justice. Once that was over, she had shown everyone, including her chauvanistic Director Jones, that she was certain to become Unity's best agent.
Archer is 25 years old when we first meet her; she is extremely athletic and quite attractive with above-the-neck length brown hair and brown eyes.