In the spring of 1523, Cardinal Wolsey's 'beloved' nephew, Benjamin Daunbey, and the latter's rapscallion servant, Roger Shallot, are summoned to London. A Florentine envoy, Lord Francesco Abrizzi, has been foully murdered in Cheapside. He has been shot in the head by a new-fangled hand cannon and King Henry is determined to unmask the perpetrators of this outrage.

En route to court, Benjamin and Shallot are to collect an old court physician, Sir Edward Throckle. However, arriving at the lonely manor house, they find Throckle's corpse floating in a bath of blood - he has apparently committed suicide.

In London, Shallot experiences King Henry's rage and spite, the insults of the Abrizzis and a murderous attack on his own life. Shallot, a born coward with the fastest legs in Christendom, just wants to crawl away and hide, but the King and Wolsey are most insistent: Shallot and Benjamin are to journey to Florence, discover the identity of Lord Francesco's assassin, deliver a secret message to the Medici ruler of the city, and inveigle back to England a Florentine painter. It sounds simple enough - but the reality is murderously different, and the result will change England and Europe forever.