The Lady's Code

Description for THE LADY'S CODE by Samantha Saxon:

After her reputation is ruined by a vengeful enemy of her disreputable father, Lady Juliet Pervill's future is bleak. But rather than buckle under society's scorn, she decides to offer her services to the Foreign Office, putting her brilliant mind to work decrypting French codes.

Struggling with a mysterious new code, Seamus McCurren is shocked when the Foreign Office calls in another cryptographer--and a woman at that. His intellectual pride takes a beating, but that's nothing compared to what awaits his heart. For Seamus finds himself incredibly--and dangerously--distracted by Lady Juliet and her provocative mathematical theories, putting both of them at risk from a seductive spy master operating right in their midst...

This is #3 in Lady Spies Series.