Quan is a humble London businessman whose long-buried past erupts in a revenge-fueled vendetta when the only person left for him to love – his teenage daughter – dies in an Irish Republican Army car bombing. His relentless search to find the terrorists leads to a cat-and-mouse conflict with a British government official whose own past may hold the clues to the identities of the elusive killers.

A detective team apply new techniques to old crimes as they solve cold cases.