In Regency London, slum orphan Elle is bought by Duke Alistair Belgrave to impersonate his half-sister "Estelle" and marry Percy Vane, freeing Alistair from a forced engagement with the obsessive Beatrix Vane. What begins as a cold transaction turns into forbidden desire as the fake siblings fall for each other, complicated by a secret execution order Alistair prepared for Elle. When Beatrix exposes Elle's true identity at her engagement ball, scandal erupts and Elle flees, convinced Alistair planned to kill her. As Beatrix closes in with a gun, Alistair takes a bullet for Elle and confesses: the order was never signed. They discover matching childhood scars proving fate bound them long before the bargain.
