1653. The long, bloody English Civil War is at an end. King Charles is dead and Oliver Cromwell rules the land. Richard Treadwell, Royalist, exile, and now soldier for the King of France, burns with revenge for those who deprive him of his family and fortune. He returns to England in secret to assassinate Cromwell.

But his is not the only plot in motion. A secret army run by a deluded Puritan is bent on the same quest, guided by the Devil's hand. When demonic entities are summoned, Treadwell finds his fortunes reversed: he must save Cromwell, or consign England to Hell...

But first he has to contend with a wife he left in Devon who believes she's a widow, a furious Parisian mistress who has trailed him to England, and a young Musketeer named d'Artagnan, sent to drag him back to France. It's a dangerous new Republic, for an old Cavalier coming home.