New York, late 1840s and in the wild, noisy, brash and beautiful circus of Silas P. Swift a shadowy, mesmeric woman entrances crowds because she can unlock the secrets of troubled minds. Above them all her daughter sweeps and soars: acrobat and tightrope-walker. People cannot take their eyes from the mysterious woman in the Big Top who can help so many others, but she cannot unlock dark, literally unspeakable, memories of her own. In London memories fester in the mind of an old and venomous duke of the realm. He plots, with an unscrupulous lawyer (and a huge financial reward) against the mother and the daughter: to kill one and to abduct the other and bring her across the Atlantic to him. The actress and mesmerist Cordelia Preston and her daughter Gwenlliam live with their unusual family in the exciting new city among exciting new ideas: the telegraph, the daguerrotype, anaesthesia, table-tapping. And among the dangerous street-gangs of New York also, whose raw violence meets Cordelia and Gwenlliam and those that they love, with unexpected results.