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.

Allie Henshall and Gavin Ferraday are partners in love and business. They own Henshall Ferraday hair salon, where Allie's sisters Darcey and Sydney work alongside them. As Allie and Gavin consider taking over a vacant property across the road, they are rocked by the news that a rival hairdresser has bought it. To make matters worse, Allie discovers that the new salon, Blade Runner, is run by her ex, Finn, and his wife, Mia Bevan. Finn fathered the child Allie claimed to have aborted. He left her when he found out she was pregnant, but he's back in town to try and woo Allie.

Plagued by endless visions and nightmares, Jenny Adams suspects that, as a child, she was responsible for the brutal murder of her own mother.

A young woman joins a group of protesters trying to stop the construction of a highway through a forest with the purpose of having sex with their leader. But when morning comes and the authorities show up to disband the protesters, she hits a man with a log. This causes the two to have to go on the run. With the help of a sickly, but sympathetic woman, the two slip through police roadblocks. Traveling with her, they learn she is an ex-army lesbian who just wants to see a final sunrise at the Orkney Islands before her death.