Sixteen-year-old Charlotte Sycamore lives in Buckingham Palace and is hiding her secret identity. Surrounded by scientific inventions and mechanical creatures of Victorian London, Charlotte trusts only her closest friends with the truth.

Charlotte's father, private physician to Queen Victoria, is unaware that his seemingly timid daughter is the treasonous thief that he and Scotland Yard seek to capture. She’s wanted for stealing medical supplies from Her Majesty to treat the poor of London. It's the same thief they accuse when two of the Queen's most valuable horses are stolen. A reward is placed on Charlotte's head.

Torn between her dutiful love for her father and the blossoming, confusing feelings she has for her daring ally, Peter, Charlotte sneaks out of Buckingham Palace with the help of her trusted friends. It’s up to Charlotte, Peter, Benjamin, Adam, Polly, and Jillian to sword fight through the gaslit streets of London and travel halfway around the world in an experimental device to locate the horses, bring the true criminal to justice, and to never reveal Charlotte's true identity.