A doctor and his girlfriend are stalked by a woman who claims to be in love with him. Meanwhile, the man falls in love with a younger woman. Based on a true story

Tense drama series about the different challenges faced by the British Security Service as they work against the clock to safeguard the nation. The title is a popular colloquialism for spies, and the series follows the work of a group of MI5 officers based at the service's Thames House headquarters, in a highly secure suite of offices known as The Grid.