Scoundrel by Elizabeth Elliott

Scoundrel is a rip-roaring romance set in Regency England. Lady Lily Walters must hide her identity as a master cryptographer and so acts the flirtatious, empty-headed chit. The Duke of Remmington, notorious ladies’ man, is a master spy. Neither knows about each others’ “work”, although the Duke does realize Lily is infatuated with him. Their…