Dangerous Passions by Kat Martin

SHE'S COURTING DANGER...
When Elissa Tauber learns of her beloved brother's murder and that her native homeland is threatened, she is determined to expose the traitor. Posing as a recently widowed countess, she moves through the glittering world of the court, willing to barter even her lovely body if she must.

CAN SHE FIGHT DESIRE?
More than one man poses a threat, but it is the tall, imposing Lord Wolvermont, Colonel Adrian Kingsland, who endangers her heart. Even as she suspects he might be the spy called the Falcon, she longs for his touch. When fate takes a hand, Elissa must decide whether to betray her mission-or lose the man she loves.