At a squalid flat near the Cardiff docks, an early morning police raid goes catastrophically wrong when the police aren't the only unexpected guests. A plain clothes officer is shot dead at point blank range, the original suspect is left in a coma. The killer, identity unknown, slips away. Young and inexperienced, Will MacReady starts his first day in the Criminal Investigation Department. With the city in shock and the entire force reeling, he is desperate to help—but unearths truths that lead the team down an increasingly dark path.