In the midst of a violent storm, the residents of Morfa Halen form a search party. Jackie and Bull discover the horrifying truth behind the crimes that haunt the town. As Bull fights for his life and Jackie faces an unbearable choice, the storm reaches its peak and Morfa's darkest secrets are laid bare.

Rising floodwater cuts Morfa Halen off from the world as another body is discovered. With the townspeople evacuating and the killer still at large, Bull closes in on the truth behind an illegal operation at the heart of all three cases. Jackie, acting alone, confronts a suspect with explosive consequences and a disappearance shocks the town.

Jackie struggles after her estranged sister returns and reignites years of guilt and betrayal, while Bull finds himself faced with two cases that are undeniably linked. A confession is made, but he suspects it has been designed to protect someone closer to home, while DNA evidence exposes a devastating truth and both Jackie and Bull must choose between protecting themselves or those they love.

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.

Convinced the disappearances of Cefin and Nessa are linked, Jackie begins an investigation of her own, but she faces pushback from Detective Bull.

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.