Tessa Phillips joined MI5 in the early 80's, joining Section K, and had been in MI5 for more than 20 years. Over that time she became hard and cynical.
Like Tom, she eventually headed up her own section in the Counter-Terrorism Unit. Everyone thought she was content to maintain her position, but she was constantly battling for the upper-hand in the office, and was no stranger to dirty tricks when she wants to get her own way.
Tessa had plenty of admirers in the office. Not least Zoe, who looked up to her slick no-nonsense style as something to emulate. However, there was more to Tessa than met the eye, as Zoe found out. While they were working on a case together, Zoe was shocked that not all of the agents Tessa had on her books were real people. Once the cat was out of the bag, Tessa didn't last long in "the Grid". MI5 is no place for traitors.