The Fatal Letter.

Ran Shu grew up in an orphanage, and her beloved sister Gu Ru Yue, made Ran Shu handicapped in order to be adopted by rich people. Later, Ran Shu married photographer Zhang Ze Yi, not knowing he's abusive and use domestic violence to make her obedient. Ran Shu wanted to escape from Ze Yi's clutches, but she fell deeper and deeper, until her sister Gu Ru Yue came to seduce her husband. Ran Shu sees the whole situation, a chance to escape from her cage, and starts plotting, using her sister and husband affair, to her own advantage.