Irene is a studious girl but often gets picked on by her step-sisters and mother. Full of jealousy, they took everything from her even her boyfriend. Consumed by rage, she decided to move out and study abroad. Before getting on the plane, a mysterious person gave her a small slip. "If you choose this, you won't regret." Little did she know, she will be trained as a secret bodyguard and agent for the most handsome CEO in the nation, Alan of H-Corp. With little experience to a killer machine, Irene's whole life changed. In the whole process, Alan fell in love with her one day at a time. What will Irene's sisters do now? Will Irene be able to take revenge on those who hurt her?