Student Saara wins a coveted internship at GCHQ, but when a significant part of the UK's internet goes down, she quickly finds herself operating on the frontier of high-stakes cyber warfare.

Saara finds a suspicious line of encrypted text within the virus's code and unravels a dubious invitation. Is she getting closer to the truth or falling into a trap?

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.

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.

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.

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?