Morfa Halen is a tight-knit Welsh town precariously nestled between towering mountains and a fast-encroaching sea that threatens its very existence. As a once-in-a-generation storm begins to gather far out at sea, former detective turned teacher Jackie Ellis (Reilly) discovers the body of her 8-year-old pupil, Cefin, seemingly drowned. The discovery sends shockwaves through the community, reviving the ghost of an unsolved cold case that rocked the town three years prior - the disappearance of Jackie’s niece, Nessa, which cost her career.