Olympic marksman Seung-a becomes an assassin to avenge her sister's murder, all while balancing her dark destiny between two captivating women. Inside her vigilante squad, she fights a growing passion for her intense team leader, Sihyeon. At her cover job as a bookstore employee, she yields to the seductive charms of Yurim, a stunning regular customer. As both relationships deepen, a devastating secret looms over their heads. The alluring Yurim is secretly the cold female mastermind behind a dangerous plot, forcing Seung-a into a deadly choice between her partner and her enemy.