Sally and Ward Digburn are agents for the British Secret Service.
As the series opens, Sally Dean is a Detective-Sargeant with Scotland Yard's legendary Ghost Squad, an elite force in the police organization tasked with investigations far outside the normal criminal elements. The officers go deep undercover, usually unknown to most of the force, to ferret out gangs, con artists, and even spies. Their people keep a low profile to better maintain their anonymity. Dean has been a policeman with this division for several years as evidenced by her rank.
Howard Digburn, nicknamed Ward, is a successful stockbroker from a well-to-do family. They met on a cruise that he was taking for amusement and she was taking while on a case. [There is no reference to a book before the listed Secret Dragnet but the writing makes it feel like one before existed]. They dated for a while and quickly fell in love. He proposed but her work made her worried about committment so as of the start of the series they were a couple but not yet engaged.
The key aspect to Ward Digburn was that while he worked as a stockbroker and Dean saw nothing in his mannerisms to indicate anything else, it is revealed half way into the first book that he was ofttimes more than a white collar worker and that he, on occassion, helped out an agency of the government. It seems that his experience during the war as part of Military Intelligence and his contacts in High Finance made him an attractive man to call when the clandestine world melded into the business sector.
Dean was not wholly surprised but less than pleased to find that her boyfriend, a man who just happened to arrive in places where she could use a hand, was a handy man to use.
From the second book on, both are operatives who choose to work together more often than apart. Ward Digburn is definitely a man of action while Sally, no slouch herself in such matters, is also the thinker. Together they make a great team.