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.
Starring Peter Firth, Hugh Simon, Nicola Walker, Rupert Penry-Jones, Miranda Raison, Hermione Norris, Rory MacGregor, David Oyelowo, Richard Armitage, Keeley Hawes