Heeseung, a young man in his early twenties, stumbles upon his sister Yeeseo's classroom one day, discovering a group of deaf students, including Sunoo. As he spends time with them, helping out in his sister's absence, he gradually learns sign language. However, tragedy strikes during a school solidarity party when Heeseung finds his sister stabbed, with Sunoo nearby holding a knife. Misinterpreting the situation, Heeseung believes Sunoo to be the culprit and enacts a plan with his family to buy Sunoo from his parents and coerce him into marriage. Sunoo suffers abuse and mistreatment at the hands of Heeseung's family, while Yeeseo remains unaware of the turmoil. Over time, doubts start to surface in Heeseung's mind, leading to a revelation of Sunoo's innocence and a shocking twist in the true identity of his sister's attacker. Determined to make amends, Heeseung confronts his family, ready to seek justice for Sunoo and rectify his grave mistake.