It is 1648 and Britain is at war with itself. The Royalists are defeated but Parliament is in turmoil, its power weakened by internal discord.

Royalism's last hope is Sir Mortimer Shay, a ruthless veteran of decades of intrigue who must rebuild a credible threat to Cromwell's rule, whatever the cost.

John Thurloe is a young official in Cromwell's service. Confronted by the extent of the Royalists' secret intelligence network, he will have to fight the true power reaching into every corner of society: the Comptrollerate-General for Scrutiny and Survey.