When her father dies, Eliza Scarlet finds herself facing a difficult choice. As an unmarried woman, she faces poverty without a husband to provide for her - unless she takes on the challenge of running her late father's detective agency, which would be unthinkable for a respectable Victorian lady. Fortunately, she finds an unlikely partner in the unconventional Detective Inspector William Wellington of Scotland Yard, known as `The Duke', and the pair begin to tackle the crimes and mysteries of Victorian London together.