It's lady's maid Louisa Cannon's wedding day, but the fantasy is shattered shortly after when she is approached by a secretive man asking her to spy on Diana Mitford--who is having an affair with the infamous Oswald Mosley--and her sister Unity. Thus as summer 1933 dawns, Louisa finds herself accompanying the Mitfords on a glitzy cruise, full of the starriest members of Society. But the waters run red when a man is found attacked. Back in London, the case is taken by lawyer Tom Mitford, and Louisa finds herself caught between worlds: of a love lost, a family divided, and a country caught in conflict.