The Undeclared War

Parvin has just started a one-year student-placement at GCHQ when a cyber-attack takes down some of the UK Internet and she joins the team examining the code of the malware. She is praised when she discovers a second attack within the code and a diligent search for a third attack doesn't find one.

Meanwhile, she feels alienated within GCHQ but makes friends with John Yeabsley, who spends his lunch-time correcting the grammar of other people's blogs. He, in turn, says how alienating it is to not be able to talk about his work outside. It is later shown that Parvin has not told her family where she is working and her brother is appalled when she finally tells him.

Trusov had attended a class with Parvin in London and when he returns to Russia he starts working for Russia's Twitter-misinformation campaign, but when the UK crash the facility as reprisal for the malware he reluctantly joins the offensive malware department.

Russia escalates the attack and incites unrest in the UK by interfering with the reporting of a general election, whereupon the UK remotely cyber attacks some Russian arms companies. Russia exaggerate the damage and uses it as a pretext for isolating GCHQ from the NSA by leaking NSA software from a UK site.

Trusov eventually reveals that this was all planned by Russia and he deliberately and openly leaks all the Russian software to GCHQ as a gift that the UK can use to appeal for help from the USA just as the tit-for-tat reprisals become overtly physical. In the last scene, Parvin stands stricken with grief because Trusov has sacrificed himself.

• Hannah Khalique-Brown as Saara Parvin, a second-year computer science student
• Simon Pegg as Danny Patrick, GCHQ Head of Operations
• Maisie Richardson-Sellers as Kathy Freeman, an NSA analyst detailed to GCHQ (series 1)
• Edward Holcroft as James Cox, a teacher and Saara's live-in boyfriend (series 1)
• Adrian Lester as Prime Minister Andrew Makinde (series 1; guest series 2)
• Alex Jennings as David Neal, Director of GCHQ
• Mark Rylance as John Yeabsley, a longtime employee of GCHQ (series 1)
• Alfie Friedman as Gabriel Davies, a GCHQ mathematician and code breaker (series 1)
• Kerry Godliman as Angie McMurray, the head of Russia Global News (RGN) in the UK (series 1)
• German Segal as Vadim Trusov, a Russian programmer, and the son of a wealthy and influential Russian arms dealer, from whom Vadim is estranged
• Joss Porter as Phil, a GCHQ analyst
• Tinatin Dalakishvili as Marina Veselova, a Russian journalist and single mother (series 1)
• Tom McKay as Max Kelly
• Ed Stoppard as Richard Marston, the newly elevated Foreign Secretary and a constant thorn in Danny’s side
• Siân Brooke as Barbara Napier, Danny’s wife, ex-MI6 and now an analyst at GCHQ (series 2)
• Danny Sapani as Charlie Francis, GCHQ’s Head of Security and Danny’s childhood friend. (series 2)
• Chloe Pirrie as Lt Colonel Roz Cavendish, seconded by Marston to GCHQ in the newly created role of Director of Rapid Response, a move which Danny interprets as a threat to his authority (series 2)
• Jason Tobin as Nicky Chan (series 2)
• Gavin Spokes as Alex Sheldon (series 2)

The music in the series was assembled by Debbie Wiseman and most notably included in several places throughout the series a folk adaptation of the Cossack lament written by Nikolai Verevkin, Under the green willow (or Black Raven). The version in the show was provided by the London-based singers Evelyn Bates and Violet Verigo whose rendition is influenced by Pelageya's performance.^[10]

In the United Kingdom, the first series aired from 30 June 2022 on Channel 4.^[3] The second series in full premiered on 21 July 2026.^[6]

In the United States, the first series was released on Peacock on 18 August 2022.^[1][11] The second series is due to premiere on 27 August 2026.^[9]

• Cyberwarfare by Russia