 Following the tragic death of DS Mel Silver (Claire Goose), Frankie Wharton (Holly Aird) has left the Cold Case Unit to return to research. Felix Gibson (Esther Hall), a bright, strong and somewhat altruistic pathologist, has stepped into her shoes. But Detective Superintendent Peter Boyd (Trevor Eve) is finding it hard to find a replacement for Mel. In the meantime, DS Andrea Stephenson (Georgia Mackenzie), who likes to be known as Andy, has been drafted in, on attachment from Kent C.I.D. Six years ago, Andy found a body on top of a water tower in Kent. The case bears similarities to a mummified body discovered on a derelict aeroplane. Meanwhile, Spencer Jordan (Wil Johnson) goes undercover in prison. His mission is to discover the reasons behind these deaths from the convicted killer, who is too scared to say anything. But the man commits suicide in prison before Spencer can get him to reveal the identity of the true killer. The plane victim s uncle arrives from India to tell the team that his nephew was investigating a corrupt businessman who had been peddling fake drugs. The shadowy figure of the corrupt Indian businessman grows increasingly sinister as the team discover that he was manufacturing fake pharmaceutical drugs designed to be sold at a high price to unwitting Aids victims in third world countries. A major international pharmaceutical company is implicated in the cover-up and it becomes clear that they will take steps, however illegal, to silence their problem.