Táto séria sleduje osudy mladej ženy, ktorá sa zapletie do sveta tajných misií a dobrodružstiev. Odohráva sa vo viktoriánskom období s dôrazom na atmosféru. Dej sa točí okolo odhaľovania tajomstiev a riešenia zapeklitých prípadov, ktoré preveria odvahu a dôvtip hlavných hrdiniek. Ide o napínavé čítanie plné intríg a akcie.
Rescued from the gallows in 1850s London, young orphan and thief Mary Quinn is offered a place at Miss Scrimshaw's Academy for Girls where she is trained to be part of an all-female investigative unit called The Agency and, at age seventeen, she infiltrates a rich merchant's home in hopes of tracing his missing cargo ships.
A follow-up to A Spy in the House finds mid-19th-century orphan Mary Quinn tackling a latest case in which her efforts to discover a murderer's identity force her to relive harrowing childhood experiences.
When Mary Quinn is ordered to work undercover after a petty thief steals from Buckingham Palace, she receives attention from a prince, wonders at a murder suspect's shared name with her father, and struggles with her feelings for James Easton.