George Downing came of age as a Puritan pioneer in colonial Massachusetts, before crossing the Atlantic to sign up for the English Civil War. He fast became Oliver Cromwell's chief of military intelligence and was later a diplomat and an MP. However, Downing spectacularly switched sides, shamelessly betraying his friends. He prospered under Charles II, yet he remains one of the most elusive figures of his age. In Turncoat he emerges as the extraordinary - if troubling - anti-hero of his own life story.

Judged by contemporaries to be 'a fearful gentleman' and a 'perfidious rogue', Downing was a double-dealer who bribed and blackmailed his way to diplomatic success across Europe; and, when it was expedient, betrayed friends to horrifically violent deaths. He pioneered the practice of judicial kidnapping known today as 'extraordinary rendition', was a booster of the Atlantic slave trade and had a hand in starting two major wars.

Always at the centre of events, Downing engaged with the most illustrious men and women of his times. His patrons were Oliver Cromwell and King Charles II. 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 follows George Downing from the asceticism of Puritan New England, across English battlefields, through courts, chancelleries and parliaments, to the fleshpots of Restoration London, where he would spend his final years in unrestrained indulgence as one of the richest men in the kingdom.