Samantha 'Sam' Gunn is an agent with the CIA.
She will be, as her saga progresses. Initially she is living a totally different sort of life in a totally different part of the world, namely the Philippines. And rather than working in something like espionage, she helps run a shelter. Then she meets a fellow names , an operative with the CIA, and gets involved with his current mission and with him personally and that changes her life and its trajectory completely. Well, to be honest, she was already moving towards the thick of things when Noble showed up as her best friend had been kidnapped by a very nasty local gangster and Gunn was determined to get her free. As we are told, "she had taken the law into her own hands and proved her courage in a firefight that would have reduced most grown men to Jell-O".
We are given a nice summation of her early on with: "Samantha Gunn. Age twenty-four. Born in San Diego, California. Father is a US citizen. Mother is from Hong Kong. Ms. Gunn has dual citizenship. She was on the women's rowing team in college, and according to her social media, she likes to ice skate. She graduated Yale. Moved to Manila. Works at the shelter run by Bati Ramos."
The offer to her to become an operative herself came as a surprise as she was recovering from her adventure. "After Hong Kong, joining the Company had seemed like the next logical step. She had always been a fan of thrillers. She devoured mysteries by the armload, reading as many as fifty books a year. Meeting Jake and helping him rescue Bati had given her a taste of the real thing. Suddenly, working a 9 to 5 job was impossible. She had spent her time in the hospital, recovering from a gunshot wound, wondering how she would ever return to a normal life. She had looked into the police, the military, even the FBI. It wasn't exactly what Jake did, but it was close and she would get to solve crime. She was all set to submit her application to Quantico when [the offer came]."