Lee Seon-yoo is training to become a nun. Right before she finally gets her wish, she learns that her beloved older sister Jin-yoo has died. Jin-yoo was betrayed and killed by her lover, Jang Tae-jung. Tae-jung, a smart, good-looking man from a humble background, had committed himself to luring and marrying a tycoon's daughter "against all odds," as part of an effort to get him into the upper class of society.

Seon-yoo then meets Seo Ji-seok, an immature man from a rich family whose sister Ji-hee is married to Tae-jung. Ji-seok is at risk of losing the inherited family business to Tae-jung and Ji-hee, since Ji-seok's mother is the family patriarch's second wife.

To take revenge on the man responsible for her sister's death, Seon-yoo gives up her dream of becoming a nun. She marries Ji-seok, and becomes Tae-jung's sister-in-law. Thus, Seon-yoo begins leading a double life: she pretends to be the ideal wife and daughter-in-law in front of the Seo family, and only takes off her mask in front of Tae-jung, proving she can be just as ruthless and vicious as Tae-jung. Seon-yoo wears her angel wings while hiding the dagger of revenge.