Sarah Jensen is a financial trader.
She is a very successful one, considering she is in her late twentys when the two-book series starts. She makes over £500,000 a year in salary and bonuses and is very well respected by her bossess and her co-workers. She is happy and largely content although much of the excitement she once felt for her high-pressure job is winding down.
Through a brother and his best friend who is also Jensen's occasional lover, she experiences second-hand the thrills and challenges of mountain climbing, a passion of her brother she largely finances. This habit of taking care of Alex is something she has had for most of her life since their parents died when she was 8 and he 6. They went to live with an aunt and she had a neighbor who pitched in to help raise them but Sarah was her brother's protector then and it continues to the present.
The neighbor mentioned, an aging gentleman named Jacob, played an important and lasting role in her development for he was a kind man who treated the children well and helped provide their daily needs when the aunt was busy with her work. Jacob was also a man who earned a better than average living stealing things. He could open most locks and many safes and did so frequently, stealing from people and companies that had insurance. Since the children knew of his occupation and learned his ethics as they grew up, this gave Sarah an interesting viewpoint on what it takes to survive.
Sarah is not a crook. She is trustworthy and dedicated to her work and would not dream of shortcutting any procedure or circumventing any laws. She has no desire to break the law. She is not adverse to bending it, though, and sometimes bending it a lot.
Much of this is not known to the Governor of the Bank of England nor to a major official of MI6 when they needed someone to work inside the financial system to help bring down an international crook damaging the security of the UK. They needed someone sharp and capable and willing to help. She was definitely that. She was just a lot more they did not know about.
The second recorded adventure of Jensen does not have her working for the government but contacts she made and lessons she learned did come into play.