Judged by contemporaries to be a 'perfidious rogue', Sir George Downing rose to prominence during the English Civil War as Oliver Cromwell's chief of military intelligence. In the Interregnum he proved himself a double-dealer who bribed and blackmailed his way to diplomatic success across Europe (pioneering the practice of judicial kidnapping and starting two major wars in the process), before spectacularly betraying his friends to horrifically violent deaths by defecting to Charles II's court.

Always at the centre of events, Downing engaged with the most illustrious men and women of his times: Samuel Pepys was his clerk; John Milton prepared his letters and dispatches; William of Orange was godfather to his son; his next-door neighbour was Queen Elizabeth of Bohemia; and when Downing finally built his street, his surveyor was Sir Christopher Wren.

Turncoat tells George Downing's story for the very first time, following him from the asceticism of Puritan New England, across English battlefields, through courts, chancelleries and parliaments, to the heart of wealth and power in Restoration London.