Lee Seon Yoo is training to become a nun. Right before she finally achieves her dream, 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 lure and marry 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.