The Inspector Lynley Mysteries (2002)

Season 4: Episode 3

Lynley and Havers investigate the killing of a porter at the House of Lords. At first it looks as if the murder may be connected to the dead man's gambling debts, but then a senior clerk is also murdered, with evidence of a conspiracy involving stolen test reports on a new missile system. Havers traces the missing documents, but then she finds she and Lynley are both being followed...