"Queen Victoria has a problem: there's a petty thief at work in Buckingham Palace. Charged with discretion, the Agency assigns quick-witted Mary Quinn to the case. Posing as a domestic in the royal household and fending off the attentions of a feckless Prince of Wales are challenge enough, but when the prince witnesses a murder in an opium den -- and scandal threatens the royal family -- Mary learns that the accused killer may be someone very close...

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.