Hidden Face - เล่ห์ ร้อน ซ่อน ชู้ (ซับไทยแปล google)

Su-yeon, a cellist in an orchestra led by her fiancé and conductor Sung-jin, disappears one day, leaving behind only a video recording. Sung-jin is devastated over the loss of Su-yeon, but feels a strong attraction to Mi-ju, a cellist who fills in for his fiancée. Then one rainy night, Sung-jin and Mi-ju get swept away by their mutual desires for each other and commit an unforgivable act at Su-yeon’s house. Meanwhile, Su-yeon, who is thought to have gone missing, remains trapped in a secret room inside her house, and watches the naked truth unravel before her.