1553: a harsh winter buffets the realm. Mary Tudor has become queen and her enemies are imprisoned in the Tower, but rumours of a plot to depose her swirl around the one person many consider to be England's heir and only hope - her half-sister, Princess Elizabeth.

Brendan Prescott's foe and mentor, the spymaster Cecil, brings news that sends Brendan back to London on a dangerous mission. Intent upon trying to save Elizabeth, he soon finds himself working as a double-agent for Mary herself.

Plunged into a deadly game of cat-and-mouse with a shadowy opponent who hides a terrifying secret, Brendan races against time to retrieve a cache of the princess's private letters, even as he begins to realize that in this dark world of betrayal and deceit - where power is supreme and sister can turn against sister - nobody can be trusted.

'Gortner has again produced a richly detailed book that is hard to put down.' Historical Novels Review on The Queen's Vow.