Sandra Maxwell is an agent with Special Branch.
In that organization, the members are police officers so calling one an agent is incorrect, of course. Maxwell is an Inspector in that spy-and-terrorist hunting organization when we first meet her. Thanks to her superb helping of the main character of the first recorded adventure we have with her in it, she will get promoted to Superintendent and be put in charge of the West of Scotland sector, stationed in Glasgow.
She is described initially as being "tall with dark hair and a pretty face, but with hard eyes, in her mid-thirties."
Through most of the time we follow the activities of her and her well trained team of investigators, Maxwell lives in Glasgow with her mother. They have, from the little mentioned of it, a good relationship but it is not the manner she had expected to be living during the the days just after the end of the Second World War.
That expected existence ended when "the love of her life had been killed in an RAF flying accident". In typical Maxwell honesty and abruptness, she had chafed at her church minister's attempt to comfort her with the platitude of it being God's Will. "In her grief, she'd snapped back, 'Nonsense! It was a maintenance error, and avoidable. That's not pre-ordained,' and walked out of the room in anger. In her job, she saw daily examples of lowlifes doing nasty things to innocent people. To think of all that as pre-ordained was just absurd. People were responsible for their own actions."
Maxwell is the focal point of this entry but she is by no means the only player in it. These adventures comprise both a spy series and an enjoyable police procedural as she first is part of an investigative team of spy-hunters and then becomes the head of that team. Additionally, she will need to interface with American investigators, including several men from the CIA.