Why Sister-in-Law?I'll Save the Heroine!; Why Do I Have to Be the Sister-In-Law?; 왜 하필 시누이죠?; Por Que eu Tenho que ser a Cunhada?; À la rescousse de ma belle-sœur !; Wae Hapil Sinuijyo?; ¿Por Que Soy Una Cuñada?

Imagine Lee Sangyeo's surprise when she wakes up one day inside her favorite novel... and her horror when she realizes she's in the body of the adorable heroine's evil sister-in-law, Aylee Brydon! Knowing that the story will end terribly if nothing changes, Aylee is determined to save the heroine at all costs. However, her complete character reversal leads to problems in high society and causes friction with her cold fianc, Duke Van Drave. At this rate, Aylee might be the one who needs saving!