Nicholas Saville, Viscount Redfern, has been kept busy on many missions for King George's spymaster, Sir Alaric. He's been so busy that his fiancee, Helen Barrett, is tired of being neglected for years and breaks of their engagement. Nicholas wishes he could settle down with Helen, but his family was left in financial ruin and it's only with the help of Sir Alaric, in exchange for his service, that everything isn't lost--and he can't give Helen a convincing reason for his absences.
But Sir Alaric things the notorious Hellfire League is up to something and promises Nicholas that he may be free if he succeeds in foiling the plot. And luckily for Nicholas, the powerful earl who is wooing Helen (using dark magic to enchant her), is a suspect.
Nicholas isn't a magic-user, so there isn't a strong emphasis on the paranormal in this romance, even though the bad guys are using some magic and there's a ghost. I'm also not entirely sure Nicholas couldn't have handled his relationship with Helen a bit better before being totally out of touch for years and causing her to break off the engagement... But both characters were otherwise reasonable and fairly sympathetic, although I did wish I felt for them just a bit more than I did.