Tuppence and Tommy Beresford are agents for the British Secret Service.
At least they will be after a relatively short time in the first recorded adventure. They will change occupations for a while but be brought back when their services are again needed. Being very much desiring of something different to challenge and, more importantly, amuse them, they are always more than happy to answer that call of duty. That and the need to make a living definitely appeals to them, especially at the beginning.
Over the course of this series, the years will pass and pair will age pretty much along with it. Both will be in the early 20s when we meet and well into the latter years when we see them for the last time. In the span of time they will go from being newly reunited friends to dating to getting married to having children to having grandchildren and to entering retirement.
The Beresford's make up a distinct partnership and a very good one in that both halves are vitally important for its success. But it is without much argument that the more dynamic of the two is the natural born leader Prudence Cowley, aka Tuppence. She is the daughter of a archdeacon in the Anglican church, the fifth of seven children. How she got the nickname of Tuppence is lost to history; even she had no idea how to came to be. Being far down the totem pole of offspring, she grew up with a self-sufficient air and an independent nature that does not hesitate to take charge of things.
Tommy for his part in the duo is not only a man quite capable of taking physical action when called for, he is also a glib talker with more than little bit of a con man's ability to finagle his way. He is not by nature dishonest, indeed quite the opposite, but he can be delightfully mischievous who can talk his way into and out of trouble.
We learn right off that they had both attended some school together as children and become friends but then life and time had separated them before they chanced to meet up again a few years later during the Great War when he was in the hospital from war wounds and she worked at the facility in the office and ofttimes as a driver. Then again a couple years would pass before another reuniting would take place in 1919 when they bump into each other outside a tube station in London, both having recently been 'demobbed' from their military service.
Though they would greet each other on that reunion with "Tommy, old thing" followed by "Tuppence, old bean", neither were that old; "their united ages would certainly not have totaled forty-five".
Both are in need of income as they learn while talking at a nearby tea shop. It is there they will come up with the crazy idea of starting a private detective service and Tuppence will waste no time putting an advertisement for it in the paper. That conversation will be how they would soon get involved with intelligence work.