When a young man is stabbed to death, a facial recognition expert helps Merseyside Police catch the killer. And a specialist palynologist's help is needed by detectives investigating the disappearance of an elderly couple.

A blood residue specialist leads police to the killers of an East Sussex waiter, brutally bludgeoned in his flat. And a forensic entomologist uncovers a case of extreme neglect when a Merseyside grandmother is found dead in her home.