Countess Emily Cowper was stubborn, beautiful, intensely politically ambitious and utterly brilliant. Wife to one Prime Minister and sister to another, she was once one of the most powerful people in England and changed the course of history. But her story has never been told - until now.

Born Emily Lamb, she was raised at the centre of glamorous Regency high society with its duels and dissipation. Her godmother was the infamous Georgiana, Duchess of Devonshire, and she was admired by Lord Byron and Thomas Moore. She made an early love marriage to Earl Cowper, but when it soured she took a string of lovers, culminating in taming a rake: the promising, promiscuous Lord Palmerston.

But her petticoats and parties belied a steely determination. She used her political genius to engineer her brother, Lord Melbourne, and Harry Palmerston's premierships. Once they were in Downing Street, she acted as their chief counsels, wrote speeches and memos, and schemed tirelessly to promote the Whig cause.

Written with novelistic richness and extraordinary details drawn from the hundreds of intimate letters and journals she left behind, The Countess unveils the life of this exceptional woman, and offers new insight into the time in which she lived.