According to Korean folk tradition, the 21-day period after childbirth is known as “seire.” During this time, a newborn is vulnerable to bad luck, curses, and even evil spirits. Many superstitions surround these first three weeks, and new mother Hae-mi carefully follows every one of them. Her husband, Woo-jin, reluctantly plays along, but when he attends an ex-girlfriend’s funeral, he unwittingly opens the door to dark supernatural dangers.