秘密機関
Unlike many other recurring detective characters, including the better known Christie detectives, Tommy and Tuppence aged in time with the real world, being in their early twenties in "The Secret Adversary" and in their seventies in "Postern of Fate". In their early appearances, they are portrayed as typical young people of the 1920s, and the stories and settings have a more pronounced period-specific flavor than other stories featuring more popular Christie characters. As they age, they are revealed to have raised three children – twins Deborah and Derek and an adopted daughter, Betty. Throughout the series they employ a man named Albert, who first appears as a lift boy who helps them in "The Secret Adversary", their hapless assistant at a private detective agency in "Partners in Crime," and subsequently, as a now married pub owner, renders vital assistance to the pair in "N or M?." By "Postern of Fate" he has become the Beresfords' butler and has now been widowed. In "Postern of Fate" the Beresfords also own a small dog named Hannibal.