As the true extent of Russia's interference with the UK becomes clear, Saara and her former classmate join forces. Can they uncover the hidden code and prevent a war?

Signs of irregularity in the UK general election result prompt political unrest, and the nation's relationship with its allies is threatened. Saara makes a devastating discovery.

With Danny unconvinced by Saara's exchange with a whistleblower, she's in a difficult position, but a revelation from Kathy forces Saara's hand. Meanwhile, Marina takes up a new opportunity in London.

Saara's classmate Vadim returns to St Petersburg. He reluctantly takes a covert job and soon becomes the victim of his own success as his allegiances are put to the test, leading him to a risky stunt.

Saara is put to work combing through the text in the virus, looking for passwords. It's a monotonous job, but after many hours she finds a suspicious line of encrypted text within the code. Her colleagues think it's unimportant, but Saara isn't convinced. She also gets more familiar with the players at GCHQ and makes some unlikely friends. With their help, Saara unravels a dubious invitation to rendezvous - but is she closer to the truth or just willingly entering a carefully baited trap?

A leading team of analysts buried in the heart of GCHQ, secretly works to ward off a series of cyber-attacks on the UK in the run-up to a general election. When a routine stress test of internet infrastructure goes awry, 21-year-old GCHQ intern Saara Parvin suddenly finds herself operating on the invisible frontier of high-stakes cyber warfare. In a thrilling cat-and-mouse game, Saara and the team at GCHQ must try to stay one step ahead and anticipate their opponents' every hidden move.