Harrington unites a suspected traitor with a heroic soldier in her sparkling fifth Lords of the Armory Regency (after A Relentless Rake). The Home Office tasks Capt. Nate Reed, bastard brother to the Earl of St. James, with tailing widowed Lady Sydney Rowland because of her possible connection to an assassination plot against the prince regent and the prime minister by the sinister terrorist group Scepter. When Sydney tells Nate that Scepter is blackmailing her (though she does not divulge what they have on her), Nate realizes that she's a victim of the group, rather than a member, and his desire to protect her trumps his commitment to his assignment. As Nate battles with his conscience over giving in to his escalating attraction to Sydney and forgoing the self-imposed celibacy he's maintained since the death of his wife, he works to keep Sydney safe--a task made harder by her closely held secret. Harrington vividly portrays the emotional interactions between her protagonists, highlighting their attraction while propelling the plot forward with an alluring mystery. Readers won't want to put this one down. Agent: Sarah Younger, Nancy Yost Literary. (July)