The Undeclared War

A young intern's first day at GCHQ coincides with a major cyberattack on the UK. To win her superiors' trust, she breaks rank to analyse the malware code without permission and uncovers a greater threat missed by others.

Saara 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.

Vadim takes a covert job to assert his independence and starts an affair with a co-worker. The FSB notices his talents and coerces him to work on the cyber weapon project, putting his allegiances to the test.

Marina moves to London for a new opportunity; Saara shares some information with Danny that she received from an anonymous source, but the latter remains unconvinced; Kathy informs Saara that GCHQ is about to reveal the names of the FSB coders.

Crowds take to the streets to protest against the general election result; a data leak threatens the UK's relationship with its allies; Saara is devastated to learn the identity of a mole inside GCHQ.

As the true extent of Russia's interference with the UK becomes clear, Saara and Vadim realise that only an act of ingenuity and extraordinary bravery can uncover the hidden level in the malware code and prevent a war.