Lady Lilia Cortova, renowned silk merchant by day and deadly assassin by night, all at the age of nineteen, mysteriously disappears while on a routine mission during the annual Midsummer festival. Left alone, her seventeen-year-old sister, Cassandra, must take her place, not only within the City but within the Underground's Guild of Assassins as well. But when Lilia discovers she was betrayed by none other than the Leader of the Guild, she must decide if her vengeance is greater than her love for her family, and how much she's willing to sacrifice for the same. Meanwhile, believing her sister dead, Cassandra has promised herself to the same man who deceived her sister. But when it becomes apparent that the Guild's loyalties may not lie as deep as once believed, Cass must quickly decide who to trust, and who to eliminate, if she's to discover what's truly become of her sister before the same happens to her.