MI-5 - Season 4 (2005)

Adam and Zaf are sent to Istanbul where they attempt to move a terrorist away from his extremist ideals.

Harry mourns the suicide of a retired MI-5 officer until a journalist informs Harry the officer was murdered because he'd been about to sell his autobiography and expose a lifetime of service secrets.

An attack is orchestrated by an Algerian terrorist in prison, and the decision is made to free him in order to gain more information about his plans.

Fiona goes undercover as a PR executive in order to rendezvous with the Syrian Foreign Minister, Riyad Barzali, who has indicated he wants contact with MI-5, but can't shake the constant surveillance of his secret service.

After the death of Fiona, Adam is tasked with the investigation of Oleg Korsakov, a multi-millionaire Russian investor, who the government see as the saviour of the NHS. Is his offer of financial intervention too good to be true?

As Britain teeters on the brink of war with Iran, Harry prevents an unofficial extradition of a terrorism suspect by the CIA, thinking he poses no serious threat to national security.

Ruth is visited by his partner Angela, an ex-MI5 officer, who asks Ruth for help in proving that MI5 killed Lady Diana. When Ruth refuses to help her, Angela takes matters into her own hands, visiting the Grid with a deadly proposition.