Former detective turned teacher Jackie Ellis discovers the body of 8-year-old pupil Cefin, seemingly drowned. The discovery sends shockwaves through the community, reviving the wounds of an unsolved case that rocked the town three years prior - the disappearance of Jackie's niece Nessa, which cost her career.

When an illicit operation is uncovered, unrest spreads through the town. Jackie and Bull are forced into an uneasy alliance and share information while following separate leads. Jackie uncovers a lie at the heart of the investigation that tore her life apart three years ago, while Bull is forced to wrestle with his intimacy issues. Their fragile partnership is tested when Bull makes a horrifying new discovery.