E1.
Episode 1A young intern's first day at GCHQ coincides with a major cyberattack on the UK. To win her superiors' trust, she breaks ranks to analyse the malware code without permission and uncovers a greater threat missed by others.
E2.
Episode 2Saara befriends John, a veteran GCHQ staffer, and seeks help from Gabriel in decrypting a message in the virus. Danny signs off on Saara attending a cyber conference with US agent Kathy, aware that Russian intelligence will also be there.
E3.
Episode 3Vadim returns to Russia where his allegiances are tested, leading him to a risky stunt.
E4.
Episode 4With Saara in a difficult position, a revelation forces her hand. Marina moves to London.
E5.
Episode 5Signs 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.