Dec 20, 2013 Updated: 10:28 AM
A modern, edgy drama full to the brim with passion, politics and peril. MI-5 leads us into the dangerous world of Britain's top-secret security agency, and into the lives of people who must lie, and sometimes die, for a living.
VISIT THE BBC's MI-5 WEB SITE
Ros uses herself as bait to lure whoever is responsible for murdering CIA agents. Also: Ros' mentor questions Harry's past; Ros makes a unsettling discovery.
Find out about upcoming shows, special events, and discounts.