The Room of Darkness (2012)

Sang-won's mother sends Snag-won, who is suffering from autism, to a country house in Kangwon-do and pays for it every month. The janitor of the country house makes his living from the paycheck Sang-won's mother sends. But when the paychecks stop coming, the janitor calls Sang-won's mother and asks for his pay. But when all he gets is not his paychecks but sharp retorts, the janitor feels shameful and as a revenge plans to mentally torture Sang-won.