Tato série sleduje osudy mladé ženy, která se zaplete do světa tajných misí a dobrodružství. Odehrává se v období s důrazem na atmosféru viktoriánské Anglie. Děj se točí kolem odhalování tajemství a řešení zapeklitých případů, které prověří odvahu a důvtip hlavních hrdinek. Jedná se o napínavé čtení plné intrik a akce.
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.
In a tale steeped in action, romance, and the gaslit intrigue of Victorian London, Mary Quinn’s detective skills are pitted against a cunning and desperate opponent. Mary Quinn has a lot on her mind. James Easton, her longtime love interest, wants to marry her; but despite her feelings, independent-minded Mary hesitates. Meanwhile, the Agency has asked Mary to take on a dangerous case: convicted fraudster Henry Thorold is dying in prison, and Mary must watch for the return of his estranged wife, an accomplished criminal herself who has a potentially deadly grudge against James. Finally, a Chinese prizefighter has arrived in town, and Mary can’t shake a feeling that he is somehow familiar. With the stakes higher than ever, can Mary balance family secrets, conflicting loyalties, and professional expertise to bring a criminal to justice and find her own happiness?