Here are two reviews that Joanna sent me which will tell you more about the characters and the plot.
Black Hawk is a starred review at Publishers Weekly:
Bourne mixes heart-pounding mystery and romance in her spellbinding fourth Spymaster historical romantic thriller (after 2010’s The Forbidden Rose). From childhood, Adrian Hawker spied on
Library Journal says
Attacked and badly wounded by an assassin's blade, former French spy Justine DeCabrillac ("Owl") struggles through the rain to the home of the only man she can depend on to save her, English agent Adrian Hawkhurst, her longtime adversary—and unforgettable lover. But Justine is not the only one in danger; the killer is out to bring down Hawk as well. And it will take all of their finely honed skills and wary, hard-won trust to unearth—and destroy—the elusive, brutal villain. Vivid, illuminating flashbacks fill in the missing years of our protagonists' bond, developing the passionate, deeply conflicted relationship between Justine and Hawk with unparalleled insight and craft. VERDICT Beautifully flawed, intensely human characters, a deadly puzzle, and a love that survives incredible odds combine to make this another emotionally riveting page-turner from Bourne (The Forbidden Rose), whose novels always deliver. Fans of historical romance will be all over this one.
The Black Hawk goes on sale today! I also recommend The Forbidden Rose, the story where Adrian and Justine meet. And The Spymaster's Lady is one of my all-time favorites. You can visit Joanna at her website: http://www.joannabourne.com/