The Truth Beneath (2016) on Netflix

Plot summary

Kim Yeon-hong is married to Kim Jong-chan, a politician challenging the incumbent No Jae-soon. Days before the vote, their teenage daughter, Kim Min-jin, goes missing. The couple first assume she has gone off on her own again for their attention, but Yeon-hong finds that the friend Min-jin named does not exist. At the school Min-jin attends, she hears about Choi Mi-ok, an eccentric friend of her daughter's, and that classmates bullied the two girls. Yeon-hong notices that Mi-ok, who comes from a poor family, wears a costly watch resembling her daughter's, and tells Jong-chan, who is absorbed in his campaign. Yeon-hong then gets into Min-jin's email and finds leaked exam papers sent by a young teacher.