Alexis Toles is an agent with the F.B.I.
Cassidy O'Brien is a stay-at-home mom of a six-year old boy.
Cassidy is also the ex-wife of a Congressman who is receiving death threats at the beginning of the recorded adventures. That is how the two women came to know each other and how, as the challenges increased to keep Cassidy and her son alive grew, the relationship between the two women grew until they would become a partnership.
Alex, as she prefers to be called, is an experienced agent with a history for getting the job done but also a reputation for doing things her way. Her history, though, goes considerably deeper. She possesses an eidetic memory and with that asset she has been able to learn numerous languages, including Arabic, Farsi, Kurdish, and Russian. This made her extremely useful as a terrorist hunter in Iraq.
She was a lieutenant (later a captain) serving there under a captain named Taylor and a colonel named Merrow. When their tours came to an end, they all moved on with Merrow going into politics. He became a Senator and later the President. Taylor rose at the Pentagon but was then picked to head the NSA. Alex worked there for a few years until the challenge of the FBI called and she moved over. Now having some powerful friends she can call on in an emergency, she is also there when they need help.
Cassidy is not a trained investigator and has no real interest in it but she is by no means an unintelligent woman and she observations and opinions become welcome to her lover.
Their relationship starts as yet another case when Cassidy and her former husband become threatened by frightening letters and the President asks for FBI help. The closeness will grow until they become a partnership.