A Shameless Angel - Secrets of the Zodiac, #3

The third novel in the Secrets of the Zodiac, a series of full-length historical romance novels, features darker, sexier storylines, complex characters, and international intrigue, set against the backdrop of the Napoleonic Wars. A courageous codebreaker, a gentleman with a score to settle, and a past that refuses to stay hidden... Sarah Brecknell has always had an unusual obsession with numbers. After the unfortunate death of her fiancé, she's lost her place in society, and her gift has left her alone with a dangerous secret.
Sarah must turn to a complete stranger for help--a secret agent in service to the Crown. She has already made one mistake in love. She can't afford another. Theodore Markham has plenty of secrets of his own, not least of which his occupation as a spy. Now he is hunting for a traitor. This time is different, though--the rogue was his best friend. The trail goes cold until he meets Sarah, a woman with extraordinary mathematical talents...and an irresistible charm that may be even more dangerous than his adversary.